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THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO 
ATLANTA • SAN FRANCISCO 

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THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



DISEASES 



OF 



ECONOMIC PLANTS 



BY 

F. L. STEVENS, Ph.D. 

PROFESSOR OF BOTANY AND VEGETABLE PATHOLOGY OF THE 
NORTH CAROLINA COLLEGE OF AGRICULTURE AND 
MECHANIC ARTS, AND BIOLOGIST OF THE 
AGRICULTURAL EXPERIMENT STATION 

AND 

J. G. HALL, M.A. 

ASSISTANT IN VEGETABLE PATHOLOGY IN THE NORTH 
CAROLINA AGRICULTURAL EXPERIMENT STATION 



THE MACMILLAN COMPANY 
1910 

All rights reserved 



^ 

<$># 



Copyright, 1910, 
By THE MACMILLAN COMPANY. 



Set up and electrotyped. Published September, 1910. 



*»£ 



'• Norfaaoti ^msg 
J. S. CuslTing Co. — Berwick & Smith Co. 
.Norwood, Mass., U.S.A. 



©CIA273034 



DISEASES OF ECONOMIC 
PLANTS 

INTRODUCTOEY 

Subdivisions of Plant Pathology 

Plant Diseases may be considered under five heads : — 

1. Those caused by cryptogamic parasites, fungi, bac- 
teria, and slime molds. 

2. Those caused by parasitic flowering plants. 

3. Those caused by animal parasites, insects, worms, etc. 

4. Those due to adverse inanimate environmental con- 
ditions, light, water, soil, nutriment, etc. 

5. Physiological diseases due to other internal derange- 
ment. 

Under the last head are grouped many diseases which 
undoubtedly will fall under one of the other groups when 
our knowledge concerning them is more nearly perfect. 

Owing to the entirely different nature of the causes of 
the diseases classed under these groups, their study falls 
to the lot of separate specialists : the first group to the 
mycologist and bacteriologist; the second to the botanist; 
the third to the entomologist and zoologist; the fourth to 
a large extent comes within the scope of the agronomist, 
and the last is in the domain of the physiological botanist. 

B 1 



INTRODUCTORY 



Scope of this Book 



This book treats primarily of the diseases of the first 
group only, with mention of a few of the most important 
diseases of the second, fourth, and fifth groups. A very 
brief statement regarding the nature of bacteria and fungi 
and the most fundamental facts of plant physiology are 
given in the Appendix. 



HISTORICAL 

A science of Plant Disease was an impossibility until 
knowledge existed concerning the nature of the parasitic 
organisms, the fungi and bacteria. The science of Plant 
Diseases or of Phytopathology was in its early formative 
period between 1853 and 1870, the very foundations being 
laid in the pioneer work of Berkeley and De Bary in es- 
tablishing the parasitism of the fungi, and in Pasteur's 
fundamental work on Bacteria and Spontaneous Genera- 
tion. 

To be sure some of the most conspicuous diseases had 
long been known by sight. Blight and mildew were re- 
ferred to in both the Old and the New Testament. Wheat 
rust was mentioned by Aristotle 350 b.c. and reference 
to mildew is found in King Lear, Act III, Sc. 4. There 
was even legislation regarding wheat rust as early as 1760. 
Yet there was little or no real knowledge of plant diseases 
in those times, beyond the fact that diseases existed. 

Following the pioneer publications of Berkeley and De 
Bary came the more complete treatises of Frank (1880, 
1895), Sorauer (1874, 1886, 1906), Kirchner (1890), Tubeuf 
(1894), and others. 

It was not until 1873 that plant pathology became a 
part of instruction in botany, and not until 1875 that 
special courses in pathology were given in any of the schools 
of America. 

A series of papers begun by Burrifl in 1873, another by 




C 4L** ' * •* £. 




HISTORICAL 5 

# 
I ri^ in 1875, and other publications by Bessey, con- 
tributed to the knowledge of plant disease and served 
esT $ cially to awaken interest in the problems and to attract 
%nts to this field of research. 
1 1879 Burrill, working upon the blight of the pear and 

Jle, was the first to attribute a plant disease to bacterial 
origin. His work was confirmed and his conclusions more 
fully established by Arthur. 

During the seventies from two or three workers in this 
field the number rapidly grew, augmented especially by 
the introduction of plant pathology into the Agricultural 
Experiment Stations and the United States Department 
of Agriculture in the middle eighties, until the number of 
papers published in the United States upon plant pathology 
between 1888 and 1900 is estimated at over four thousand. 
While only a few dozen American plant diseases had been 
even cursorily described prior to 1880, to-day a total of 
some 525 diseases, more than 250 of them serious, have 
been carefully investigated. 

Historical concerning plant disease prevention. — 
Though little could be done to devise rational methods 
of combating plant diseases until their causes were 
known, a very few rule-of-thumb, empirical ways of meet- 
ing them had been suggested in very early days. As 
might be expected many of the methods used were value- 
less. Thus Parkinson early in the seventeenth century 
advocated the use of vinegar to prevent canker on trees, 
and Forsyth in 1790 gave the following directions for mak- 
ing a mixture to " cure disease, defects, and injuries of 
plants." * " Take one bushel fresh cow dung, one half 

1 Lodeman, E. G., "The Spraying of Plants," p. 6. 



PREFACE 

Students of Plant Disease are naturally divided into 
twO categories. First: those who wish to recognize and 
treat diseases, without the burden of long study as to their 
causes ; second : those who desire to study the etiology of 
diseases, and to become familiar with the parasites which 
are often their cause. 

The present book is designed to meet the needs of the 
first of these two classes of readers. It indicates the chief 
prominent characters of the most destructive plant diseases 
of the United States, caused by bacteria or fungi, in such 
a way that in most cases reliable diagnoses may be made, 
though it must be recognized that in some cases certainty 
cannot be had without recourse to microscopic details. In- 
formation is given regarding the best methods of prevention 
or cure for these diseases. 

In this volume only such characters are used as appear 
to the naked eye or through the aid of a hand lens, and all 
technical discussion is avoided in so far as is possible. No 
consideration is given to the causal organism except as it 
is conspicuous enough to be of service in diagnosis, or 
exhibits peculiarities, knowledge of which may be of use in 
prophylaxis. 

While, in the main, nonparasitic diseases are not dis- 
cussed, a few of the most conspicuous of this class are 



VI PREFACE 

briefly mentioned, as are also diseases cansed by the most 
common parasitic flowering plants. 

In selecting common names for diseases the authors have 
chosen those that are most widely used or generally known. 
In default of any generally accepted name or in cases where 
the name now in use is ambiguous, as when the same name 
is applied to more than one distinct disease, they have fol- 
lowed the plan of giving to the disease a name made by 
joining to the name of the genus of the causal fungus, with 
or without elision of the last syllable, as euphony may dic- 
tate, the termination " ose," signifying " full of." They 
have also employed this more accurate mode of designation 
in the text in all cases where it seemed desirable to do so. 

F. L. STEVENS. 

J. G. HALL. 
Raleigh, N.C., 
July, 1910. 



ACKNOWLEDGMENT 

While the authors drew their information to a large 
extent from personal experience with the diseases dis- 
cussed, the descriptions are necessarily largely compiled 
and the authors wish to acknowledge their great indebted- 
ness to the publications of the various State Agricultural 
Experiment Stations and of the United States Department 
of Agriculture. In many instances the words of the orig- 
inal description are used, almost as quotations except for 
slight modification for brevity or to secure a change of 
sequence. In such cases the authors could not always 
indicate the quoted words. They desire here to record 
their special indebtedness to the writings of the following 
investigators: Ralph E. Smith; G-. P. Clinton; Mel. T. 
Cook; H. S. Fawcett; J. C. Arthur; F. D. Kern; C. W. 
Edgerton; Ernst A. Bessey; J. B. S. Norton; E. M. Free- 
man; F. M. Rolfs; Chas. E. Bessey; E. Meade Wilcox; 
Chas. Brooks; B. D. Halsted ; F. C. Stewart; H. A.. Har- 
ding; J. G. G-rossenbacher ; H. H. Whetzel ; B. M. Duggar; 
H. L. Bolley ; A. D. Selby ; Thomas F. Manns ; H. R. Ful- 
ton; E.W.Olive; S. M. Bain; L.R.Jones; N. J. Giddings ; 
H. S. Reed ; W. H. Lawrence ; J. L. Sheldon ; D. Reddick ; 
Roland Thaxter; W. G. Farlow; M. A. Carlton; W. W. 
Gilbert; G. G. Hedgcock ; Haven Metcalf; W. A. Orton ; 
Mrs. Flora W. Patterson; W. M. Scott; Erwin F. Smith; 



Vlll ACKNOWLEDGMENT 

Perley Spaulding; C. 0. Townsend ; M. B. Waite; A. F. 
Woods; B. T. Galloway; C. L. Shear; Hermann von 
Schrenk; George M. Beed; L. H. Pammell; Wendell Pad- 
dock ; P. H. Rolfs ; T. J. Burrill ; Geo. E. Stone ; Geo. F. 
Atkinson; A. B. Cordley; S. M. Tracy; E. J. Durand; 

F. D. Heald ; Nellie A. Brown. 

The authors are also deeply indebted for valuable sug- 
gestions and for helpful criticism of the manuscript to 

G. P. Clinton who read the portion pertaining to smuts, 
L. R. Jones potato diseases, J. C. Arthur and F. D. Kern 
the rusts, Erwin F. Smith, the bacterial diseases, Hermann 
von Schrenk the timber diseases, W. A. Orton and W. W. 
Gilbert the other portions of the book; though all respon- 
sibility for any errors that may occur rests entirely with 
the authors. Acknowledgment is due to Mrs. F. L. Ste- 
vens and Mrs. J. G. Hall for aid in preparation of the manu- 
script and proof. 



CONTENTS 



PAGE 

Preface . v 

Introductory .......... 1 

Historical 3 

Damage caused by Plant Diseases . . . . .12 

Symptoms op Disease ........ 14 

Prevention or Cure of Plant Diseases .... 18 

Public Plant Sanitation ........ 24 

Fungicides % 

Spraying Machinery 39 

Cost of Spraying 45 

Profits from Spraying 50 

Soil Disinfection . 54 

General Diseases . . .60 

Diseases of Special Crops 69 

Pomaceous Fruits 69 

Drupaceous Fruits 115 

Small Fruits 144 

Tropical Fruits 184 

Vegetable and Field Crops 194 

Cereals 319 

Cereal Smuts, General 319 

Cereal Rusts, General 323 

Anthracnose of Cereals 327 

Special Diseases of Cereals . .... 327 
ix 



X CONTENTS 

PAGE 

Forage Crops 377 

Fiber Plants 398 

Trees and Timber 409 

General Diseases 409 

Special Hosts 431 

Ornamental Plants . . . . . . . 451 

Appendix „ 483 

^NDEX . 493 



DISEASES OF ECONOMIC PLANTS 



HISTORICAL 7 

bushel lime rubbish from old buildings, one half bushel 
wood ashes, one sixteenth bushel pit or river sand. The 
last three are to be sifted fine before they are mixed. 
Then work them well together with a spade, and afterward 
with a wooden beater until the stuff is very smooth, like 
fine plaster used for the ceilings of rooms." Soapsuds or 
urine was used to make the composition of the con- 
sistency of plaster or paint. After being applied it was 
covered with a sifting of powder made of " dry powder of 
wood ashes, mixed with the sixth part of the same quan- 
tity of the ashes of burnt bones." 

Among the early chaff, however, there were some grains 
of wheat. Thus Robertson in 1821 said: " Sulphur is 
the only specific remedy that can be named for the 
treatment of mildew on peaches. It should be mixed 
with soapsuds and then applied by dashing it violently 
against the trees by means of a rose syringe ; " thus ad- 
vocating a remedy which, modified, is still prominent for 
this class of diseases. 

The aggressiveness of several plant diseases in Europe 
between 1878 and 1882, particularly the downy mildew 
upon the grape, which, about 1878, had invaded Europe 
from America, stimulated a search in the former country 
for effective spraying mixtures. Trials of many chemicals 
were made, but it was left to accident to suggest and to 
the genius of Millardet, of Bordeaux, France, to perfect 
the happy combination of lime and bluestone that we 
now know as the Bordeaux mixture. It was customary 
in certain vineyards to sprinkle a few rows of grapevines 
near the road with a mixture of milk of lime and bluestone 
to give them a poisonous appearance to ward off depreda- 



8 DISEASES OF ECONOMIC PLANTS 

tion of the hungry passer-by. The vines so treated in 
1882 were noted by Prillieux and Millardet to be less 
injured by the mildew than were other vines, and they 




Fig. 1. — Millardet, father of the Bordeaux mixture. 

ascribed the beneficial effect to its proper cause, the lime- 
bluestone mixture. 

While several investigators were engaged simultaneously 
in experimenting with these chemicals upon the mildew, 
it was Millardet who first planned and executed experi- 
ments and published results which demonstrated the com- 
mercial value of the lime-bluestone treatment. 

The first systematic applications of copper, and of copper 
with lime as a disease preventive, were made under the 
direction of Millardet, August 18, 1883. In 1884 the work 



HISTORICAL 9 

was repeated, and in 1885 Millardet published the first 
directions for preparing 

Bordeaux Mixture 

Water 130 liters (34 gallons) 

Bluestone 8 kilograms (17.6 pounds) 

Lime 15 kilograms (33 pounds) 

This mixture was to be shaken upon the plants with a 
broom. 

Following this demonstration came the introduction of 
an era, not yet at an end, of active experimentation with 
fungicides, wet and dry, which has already yielded results 
of incalculable value. 

In 1885 also appeared for the first time the Ammoniacal 
Copper Carbonate proposed by Professor Audoynaud of 
the Montpelier Agricultural School. 

Saunders, in the Canadian Horticulturist in 1884, sug- 
gested the use of several liquid spraying mixtures for apple 
scab, but little, if any, liquid spraying for plant diseases 
was done in America prior to 1885. 

In 1885, from Section of Mycology, Division of Botany, 
United States Department of Agriculture, appeared an 
article by L'amson-Scribner, giving directions for making 
" the copper mixture of Gironde," the primitive Bordeaux 
mixture. In 1886 the spraying campaign may be said 
to have been well started in this country. 

The disinfection of seeds by bluestone was practiced 
first with the cereals as early as 1807 by Prevost of France, 
and improved by Dreisch in 1873, by the addition of a 
limewater bath to follow the bluestone. In 1887 Jensen 



10 



DISEASES OF ECONOMIC PLANTS 



of Denmark improved upon these methods by develop- 
ing his hot-water treatment, which has since proved of 
—. great value, not so much for its 
primary use, in which it has been 
superseded by formalin, but ow- 
ing to its applicability to those 
loose smuts which cannot be suc- 
cessfully treated by surface disin- 
fection. Similar seed treatments 
have been extended to the potato 
by Bolley, and to cabbage by 
Harding. 1 

The production, by breeding, of 
new and disease-resistant varieties 
is one of the latest and most prom- 
ising methods of combating plant 
diseases. Grapes resistant to Phyl- 
loxera were produced by Mil- 
lardet; others resistant to coulure 
by Pierce; cotton, cowpeas, and 
watermelons resistant to wilt by 
Orton. 
No small part in the progress that has been made in the 
prevention of plant disease is due to the improvement of 
appliances, dusters, pumps, nozzles, etc., for distributing 
the disinfectants upon the plants. This progress is well 
illustrated by comparing the broom of Millardet with the 
knapsack, barrel, or power sprayer of to-day. 




Fig. 2. — An improved brush 
for distributing Bordeaux 
mixture. After Lodeman. 



. * Harding, H. A., and others, -N. Y. (Geneva) Agr. Exp. Sta. Rpt. 23, 
pp. 62-78. 



HISTORICAL 11 

Important Events in Plant Disease History 

Ancient. Recognition of the existence of plant diseases in early- 
Biblical times. 

1683 The discovery of bacteria. Loewenhoek. 

1807 The efficiency of copper against smut spores discussed. 
Prevost. 

1821 The use of sulphur as a fungicide recommended. Robertson. 

1845 The use of boiled sulphur and lime for mildew advocated. 

1846 The studies of Rev. M. J. Berkeley. 

1853 The beginning of the " Morphology and Physiology of the 
Fungi" and the proof of parasitism of fungi. De 
Bary. 

1861 The publication of the first American paper on plant pa- 
thology. Engelmann. 

1860-1864 The founding of bacteriology. Pasteur. 

1864 The proof of alternation of hosts, hetercecism. De Bary. 

1869 The first university publication in America regarding plant 
pathology. University of Illinois. 

1873 Plant pathology taught incidentally with botany in Amer- 
ica. Burrill. 

1875 Plant pathology first taught as a special subject in America. 
Farlow. 

1879-1880 Proof of bacterial disease in plants. Burrill. 

1880 The discovery of the cyclone principle in nozzles. Barnard. 

1882 The beginning of "Sylloge Fungorum." Saccardo. 

1884 Systematic introduction of plant pathology into American 

Agricultural Experiment Station work. Arthur. 

1885 The announcement of the Bordeaux mixture. Millardet. 
1885 Organization of a Section of Mycology in the Division 

of Botany, United States Department of Agriculture. 
Lamson-Scribner. 

1887 The hot- water treatment for smut. Jensen. 

1888 The introduction of formalin as a disinfectant. Trillat. 



12 DISEASES OF ECONOMIC PLANTS 

1888 Organization of the State Agricultural Experiment Stations. 
1890 The beginning of pump improvement for spraying. 
1906 The passage of the Adams Act. 



DAMAGE CAUSED BY PLANT DISEASES 

The crop grower, in his ignorance of what plant diseases 
are, often suffers much damage from them, entirely uncon- 
scious of the fact that his crop is affected by disease. Or, 
if the presence of disease is recognized, the amount of 
damage is often underestimated. Thus oat smut to the 
extent of 15 or even 40 per cent is sometimes entirely over- 
looked by an otherwise observant man. 

An attitude of willful disbelief in the prevalence of a 
disease is often couched in such terms as these : " I don't 
see why I must work to protect my apples from rot. My 
grandfather used to raise fine apples without any attention 
to these things." 

It must be recognized that plant diseases are with us; 
that they are increasing by importation from other coun- 
tries or other states ; that diseases formerly insignificant 
are, in many instances, becoming serious ; that long, inten- 
sive culture of one crop in a locality permits new diseases 
to develop. Diseases have many means of dispersal : on 
seed, hay, or other produce shipped by mail, express, or 
freight ; on animals ; by wind ; by water ; by birds. Dis- 
eases will continue to spread and to increase in destructive- 
ness until the individual and the general public are aroused 
to such active appreciation that conditions of plant sani- 
tation and plant protection become much more general 
and effective than they now are. 



DAMAGE CAUSED BY PLANT DISEASES 13 

Aside from diminishing the value of the produce and 
the thrift and future productiveness of perennials, as 
trees, vines, etc., plant diseases entail depreciation in the 
value of land, and in some cases even occasion large loss 
of life. Thus the famous famine in Ireland in 1845 is 
directly traceable to the injury done to the potato crop 
by the potato blight. The presence of ergot in grain 
used as food for cattle or man may result in disease and 
death. 

The presence in land of the causal germ of the melon, 
cowpea, cotton or tobacco wilts, of onion smut, cabbage 
club root or black rot, or of any one of many other soil- 
borne diseases precludes the possibility of successful culture 
of the susceptible plant for a long period of years, perhaps 
forever, upon the soil in question. Such restriction may 
prevent the raising of just the crops that are most profitable 
in that particular section, and in some instances depreciation 
of 50 per cent or more in the market value of land has resulted 
from the invasion of one of these ineradicable soil diseases. 
Still more serious is this kind of injury if the crop in ques- 
tion is one which requires large money outlay before the 
presence of the disease germs is manifest. In the case of 
Sumatra tobacco under shade, or lettuce grown under 
canvas, the money expended to prepare for the crop may 
aggregate from $700 to $1000 or even more per acre the 
first year. The capture of such acreage by the lettuce 
drop or the tobacco wilt is a far more serious matter than 
a plant disease is usually considered to be. Some of the 
money losses caused by diseases of a few crops are given 
below, merely as illustrative instances. The authority is 
named with each estimate. 



14 



DISEASES OF ECONOMIC PLANTS 



The California vine disease in 1892, $10,000,000. Pierce. 

Wheat rust in the United States, 1898, $67,000,000. Galloway. 

Wheat rust in Illinois, 1885, $1,875,000. Burrill. 

Violet, leaf spot in the United States, 1900, $200,000. Dorsett. 

Peach leaf curl in the United States, 1900, $2,335,000. Pierce. 

Potato late blight in New York, 1904, $10,000,000. Stewart. 

Oat smut in the United States, annual, $6,500,000. Orton. 

Wheat loose smut, United States, annual, $3,000,000. Orton. 

Wheat bunt in the United States, annual, $11,000,000. Orton. 

Potato blight in the United States, annual, $36,000,000. Orton. 



SYMPTOMS OF DISEASE 

Every part of a plant — root, stem, leaf, flower, fruit, 
bark, wood, veins — is subject to disease, and the same 

disease may be mani- 
fest in many, even 
all, of these parts at 
once. 

Rot is perhaps the most 
common symptom 
of disease to be 
noted in any plant 
part. Rot is of 
many characters, 
— soft, wet, dry, 
hard, offensive or 
inoffensive of odor. 
Blight is a symptom 
often exhibited 
by leaves, roots, stems, flowers, or fruit. It indi- 
cates complete death of the part affected, may be 




Fig. 3. — Cowpea leaf spot (amerosporiose) . 
Pycnidia scattered throughout, x 4. Original. 



SYMPTOMS OF DISEASE 



15 



local or general, and 
may or may not be fol- 
lowed by rot. 

Wilt of stems or leaves is 
caused usually by either 
a plugging, or other in- 
terruption, of the sap- 
carrying veins, or by 
some injury to the ab- 
sorbing root system. 

Spots of leaves, bark, or fruit 
may be caused by local 
blight, rot of tissue, im- 
perfect coloration, or by 
local over-development 
or under-development 
of color. 

Scab in fruit, leaves, or bark 
is due to the growth of 
the causal parasite upon 
or near the surface, or to 
or layers of tissue caused 






Fig. 4. — Sori of rust of asparagus. 
Original. 

thickening of the outer layer 
by the irritation of a parasite. 




Fig. 5. 



Hyphae in a leaf spot much enlarged. Redrawn after Garman. 



16 DISEASES OF ECONOMIC PLANTS 

Mildew upon any plant surface consists of a whitish pow- 
dery fungous growth. 

Burn is a general term applied to all cases where the leaves 
turn red or brown, especially if the edge first shows 
the symptom. 

Smut consists of a mass of spores, usually black and pow- 



:/. -■&&* » 




Fig. 6. — Clustercups of rust enlarged. After Clinton. 

dery. It is most common in the ovaries and other 

floral parts of the cereals. 
Rust should properly be applied only to cases where the 

special rust fungi (Uredinales) are present. Rusts 

usually show the spores in sori. 
Yellowing of leaves, due to diminution in green coloring 

matter, is a common symptom of disease. 
Chlorosis is a lack of proper green, a whitening of tissues 

which should be normally green. 
Canker consists of a roughening or splitting of the bark. 



SYMPTOMS OF DISEASE 



17 



In addition to the somewhat general characters accom- 
panying diseases, it is necessary for purposes of diagnosis to 
note closely the detail characters of each sick part. 

In a spot the color of its margin and center; its border, 
whether sharp or indefinite; whether the same upon both 
upper and lower surfaces are important items to observe. 

In a rot these same 
details, also the texture, 
soft or hard, wet or dry, 
the odor, and taste are 
important. 

In the plant, on a 
whole, it is well to note 
whether the disease is 
local or general, progres- 
sive or stationary, spread- 
ing regularly or otherwise. 

Certain minute struc- 
tures should be looked for 
upon rots, spots, cankers, 

or other diseased parts. Some of these, which may be 
recognized with the naked eye or a good hand lens, are : — 

Pycnidia or perithecia. — Small, nearly microscopic, 
covered sporiferous pustules on the surface of the diseased 
area. 

Acervuli. — Structures like pycnidia, but uncovered. 

Sori or spore clusters. 

Hyphae. — Erect, hair-like, very nearly microscopic 
growths coming from the diseased area. Their presence 
upon a white background may often be recognized by the 
dirty ashen color which they lend to the spot. 




Fig. 7. 



Sclerotia of lettuce sclerotiniose, 
natural size. Original. 



18 DISEASES OF ECONOMIC PLANTS 

Cluster cup. — The cup-like sorus in which the spring 
spores of many rusts are borne. 

Sclerotia. — Small, hard bodies variously colored, but 
usually black; masses of compact fungous threads. 

PREVENTION OR CURE OF PLANT DISEASES 

Owing to the comparatively small value of the individual 
among plants, cure of a plant already sick is seldom at- 
tempted except in the case of plants of exceptional value. 
Such value very rarely attaches to annuals or biennials; 
hence it is only with perennials, valuable vines, bushes, 
or trees, that cure of the individual is attempted, and here 
only in a few special cases. 

The burden of the effort of the plant pathologist must 
be directed toward methods of prevention, which are here 
worth far more than their proverbial ratio. 

The science of plant pathology, barely antedating 1880, 
is yet young; its founders in America are still alive and are 
still vigorous workers. In comparing this youthful science 
with its far more aged prototypes, human and veterinary 
medicine, one is astonished at the progress already made, 
rather than abashed at the multitude of diseases as yet 
unconquered. 

Among all classes of crops are diseases, single or many, 
which have given way to the control of man, many of 
them diseases of fearful destructiveness, yet which are 
now completely under the subjugation of the intelligent 
educated crop producer. 

The remedies, wi^h one or two exceptions, are entirely 
the result of patient, scholarly investigation, careful de- 



PREVENTION OR CURE OF PLANT DISEASES 19 

duction, followed by experimenting, testing, and improving. 
Such investigation is ever proceeding with increasing 
activity, and yearly new or improved methods of combat 
are devised, so that the future may with confidence be 
relied upon to see the subjugation of many of the foes that 
are as yet unconquered. 

Methods of Prevention 

All methods of prevention aim at the destruction of 
the causal organism, the diminution of its numbers, or the 
strengthening of the crop plant so as to withstand its attack. 
The various methods employed may, for convenience of 
reference, be here summarized as follows : — 

1. Killing the causal organism as it rests upon the seed. 
— Examples : oat or wheat smut, cabbage black rot. 
For this purpose the seeds (sometimes cuttings or even 
whole plants are similarly treated) are subjected to the 
action of disinfecting chemicals long enough to kill the 
organism causing the disease, but not long enough to kill 
the seeds. Chief among such disinfectants are: — 

A. Formalin (40 per cent formaldehyde). 

B. Corrosive sublimate. 

C. Copper sulphate, followed by weak limewater. 

D. Formalin gas generated in a gas-tight disinfecting 
room. 

2. Killing superficial fungi by applications upon the 
green parts of the plant. — Examples : powdery mildew 
upon grape, gooseberry, or rose. This method is applicable 
only with the purely superficial fungi, since internal pan- 
sites cannot be so reached without injury to the host plant 



20 DISEASES OF ECONOMIC PLANTS 

itself. It finds prominent application with the powdery 
mildews. The chief applications used are: — 

A. Liver of sulphur. 

B. Bordeaux mixture. 

C. Ammoniacal copper carbonate. 

D. Flowers of sulphur. 

3. Killing superficial fungi hibernating upon the bark 
of the dormant plant or plant supports. — Examples : apple 
hypochnose, peach curl. For this purpose Cleansing 
Sprays, often called dormant sprays, may be used. 
Since the parts of the host receiving the spray are highly 
resistant to their poisonous action, the sprays thus em- 
ployed may be much stronger than could be safely used 
when the plant is in foliage. For this purpose use: — 

A. Copper sulphate with lime sufficient to color. 

B. Lime-sulphur mixtures. 

4. The use of protective sprays. — Examples : grape 
black rot, apple scab. A protective spray is one applied 
to the plant upon its bark, foliage, or fruit, to kill any 
offensive germs that may fall upon its surface, or to pre- 
vent their growth upon or into the plant. Such sprays 
are distinguished from the cleansing sprays, which are 
not primarily for protection against future invasion, but 
rather for the purpose of cleaning off or killing all 
spores actually upon the plant. Protective sprays are 
usually employed when the plant is in foliage, and there- 
fore must be used with due regard to the susceptibility 
of the plant to the poison employed. The protective 
spray should be applied : — 

1. Often enough to replace any previous protective spray 
that may have been removed by rain or other means. 



PREVENTION OR CURE OF PLANT DISEASES 21 

2. To give protection to any new surface of twig, leaf, 
or fruit which has developed since the last protective spray 
was applied. 

The first protective spray should be given as soon as 
possible after susceptible surfaces have developed, and 
before the attacking organisms are expected to make their 
invasion. The time varies of course with each special crop, 
with each disease, with the climatic relations and section 
of the country. Nor can any absolute rule be laid down 
for the application of subsequent protective sprays. Fre- 
quency of rain is an important controlling factor. A fungi- 
cide, if rained upon just after it is applied and before it has 
time to dry, is much more easily washed off than is the 
case if it dries well before the rain falls. 

New tissue and new surfaces develop every day; there- 
fore theoretically to secure complete protection, sprayings 
need to be very frequent, much more frequent than is prac- 
ticable. To meet the needs occasioned by new growth, pro- 
tective sprays are usually given at intervals of from ten to 
fourteen days, though special rules must govern special cases. 

The chief protective sprays are : — 

A. Bordeaux mixture, full strength or weak. 

B. Ammoniacal copper carbonate. 

This solution possesses the advantage that it does not 
spot the fruit and may therefore be used near the period 
of maturity, when the Bordeaux mixture, owing to its 
spotting effect, would be less desirable. 

C. Lime-sulphur mixtures. 

5. Excision of the affected parts. — Examples : Ash 
white rot. Excision is resorted to chiefly in the case of trees 
which from their location or quality possess value suffi- 



22 DISEASES OF ECONOMIC PLANTS 

cient to warrant the necessary outlay of labor. It is so 
practiced as to remove the diseased wood and sufficient of 
the healthy wood to expose an entirely uncontaminated sur- 
face. The wounded surface is then treated with a strong 
antiseptic (tar, bluestone, or corrosive sublimate), and if 
the wound be deep, it is filled with cement to remedy any 
mechanical weakening incident to the operation. 

6. Removal and destruction of diseased twigs, leaves, 
or fruit. — Examples : pear blight, peach rot. The re- 
moval and destruction of diseased parts diminishes the 
number of bacteria, spores, etc., that are available to spread 
the disease and thus lessens infection. Mummified fruit 
may be picked from the plant or the ground and destroyed, 
or it may be removed by appropriate pasturage by fowls, 
swine, etc. Affected leaves in many instances may be 
similarly removed. Blighted twigs and cankers may be 
cut out at any time when they are seen. 

7. Removal, in whole or in part, of complementary hosts. 
— Examples : apple rust, wheat rust. Complementary hosts 
always serve as multiplying places for the causal parasite, 
and in some instances are absolutely essential to its hiberna- 
tion. Such complementary hosts should, when practicable, 
be removed from the immediate vicinity, and when possible, 
not allowed to exist within considerable distance, one eighth 
to one half mile, or better still, a greater distance. When 
it is not practicable to remove the host, the offending por- 
tions may be cut away, e.g. in the case of the apple rust 
the cedar balls may be removed from adjacent trees. 

8. Avoidance of disease-bearing material or material 
favoring disease. — Infection may reach hay through 
sick melon vines (melon wilt), or manure through sick plant 



PREVENTION OR CURE OF PLANT DISEASES 23 

parts (potato scab, cabbage rot, melon wilt, etc.). Soil 
may wash from one field to another and bear disease with 
it (tobacco wilt, melon wilt, etc.). 

9. Prevention of wound infection. — Examples : heart 
rots, sap rots, cankers, fruit rots. Wound infection may 
often be avoided by care in handling the plant so as not 
to wound it. In trees place ladders carefully, not roughly, 
among the limbs; avoid walking on limbs with nailed or 
hard boots, etc. Gather all fruit, root crops, etc., carefully 
to avoid breaking the skin or bruising the underlying tissue. 
In case of removal of large limbs coat the exposed wood 
with paint or tar to prevent invasion by parasites. 

10. Avoidance of susceptible varieties ; selection of resist- 
ant varieties. — There is much difference in the suscepti- 
bility of different varieties of plants. Study the different 
varieties of the crop to be raised, particularly in this regard, 
and use those that are most resistant. In case resistant 
individuals are observed among sick plants, save their seed 
carefully and test the resistance in succeeding years. In 
this way new and resistant varieties may be developed. 

11. Avoidance of diseased localities. — This is in many 
cases imperative where the soil is invaded by a germ 
inimical to the growth of crops of certain kinds, as in the 
case of cabbage black rot, cotton and melon wilt, etc. 
Similarly, low damp locations favor diseases of some crops 
(potato blight), and the proximity of certain kinds of plants 
leads to disease with others (apple rust). All this should 
be considered in the selection of land for the crop. 

12. The practice of crop rotation. — Constant growth 
of the same crop in any locality tends to increase the 
enemies of that crop. Rotation breaks the continuity 
and hinders the multiplication of the parasite. 



24 DISEASES OF ECONOMIC PLANTS 



PUBLIC PLANT SANITATION 

In addition to the means suggested above, which may- 
be applied by the individual plant producer, much can be 
done toward the eradication of these pests by the creation 
of a more enlightened public sentiment regarding them. 
So long as these diseases are regarded as natural, as inevi- 
table, no progress will be made. When it becomes gen- 
erally known that they are contagious, that they are pre- 
ventable, steps to overcome them will be generally made, 
and their increase checked. To create a much-needed, 
enlightened, aggressive public opinion is part of the duty 
of plant pathology. It may be done in several ways : — 

1. By disseminating knowledge concerning the nature 
of plant diseases, the damage they do, how to recognize 
them, and the means of controlling them. This may be 
done through the common rural schools, the high schools, 
the agricultural colleges, the farmers' institutes, and other 
educational channels. 

2. By instructive articles in the agricultural papers. 

3. By collections of plant diseases displayed so that the 
visitor may learn both the appearance and control of the 
important ones. 

Legislation which shall guard against shipment of any 
infectious material should be enacted and enforced. With 
all the advances of the past twenty years in the control 
of plant diseases we have but barely kept pace with their 
increase. Diseases will continue to increase for some 
decades yet, if not indefinitely, and increased efforts to 
control them are necessary on the part of the crop producer. 
At present many wise laws prohibiting the shipment of 



FUNGICIDES 25 

infected stock, particularly peach yellows and rosette, the 
various crown galls, and certain insect pests, are inoperative 
on account of lack of proper means of enforcement or too 
often owing to absence of the necessary sustaining public 
opinion. 

FUNGICIDES 

Bordeaux mixture. — While the early formulas for this 
mixture called for 6 pounds of copper sulphate and 4 pounds 
of lime to 22 gallons of water, and other similarly strong mix- 
tures were in use for several years, experimental evidence 
soon showed that the strength could be reduced without 
disadvantage. The chief strengths of Bordeaux now used 
are as follows : — 

Ordinary Bordeaux 

5 — 5 — 50 

Copper sulphate (bluestone) 5 pounds 

Quicklime 5 pounds 

Water 50 gallons 

This strength may be used on most plants the foliage 
of which is not especially delicate or sensitive to copper. 

Strong Bordeaux 

6 — 4 — 50 

Copper sulphate (blue stone) 6 pounds 

Quicklime 4 pounds 

Water 50 gallons 



26 DISEASES OF ECONOMIC PLANTS 

This strong solution is particularly for grapes, potatoes, 
and tomatoes; crops which possess good resistance to the 
copper of the mixture, and upon which a strong solution 
is desired. 

Weak Solutions 

2 — 2 — 50 

Copper sulphate 2 pounds 

Lime 2 pounds 

Water 50 gallons 

21 — 6 — 50 

Copper sulphate 2\ pounds 

Lime 6 pounds 

Water 50 gallons 

Plants with sensitive foliage, such as the stone fruits, 
peach, plum, cherry, and apricot, are injured by the stronger 
solutions, and very weak solutions must be used upon them. 

There is no certainty as to what strength of mixture is best. 
To most crops no damage can come from the use of as 
strong a solution as the 6-4-50, yet it is possible that all 
of the benefit can be derived from a 4-4-50 mixture. If 
so, there is loss of material through use of the stronger 
solution. This matter is still open to experimentation. 

In the preparation of the Bordeaux mixture it is well 
to have on hand stock solutions of copper sulphate and of 
lime. The stock solution of copper sulphate is made by 
dissolving a certain number of pounds of copper sulphate 
in one half the number of gallons of water. For example : 
80 pounds of copper sulphate in 40 gallons of water. Every 



FUNGICIDES 



27 



gallon of this solution contains 2 pounds of copper sul- 
phate, and the necessity for further weighing is avoided. 
This solution will remain good for any length of time if 
the water evaporated is replaced. 

In order to dissolve the copper sulphate, suspend it in 
a coarse bag near the top of the water in a barrel. In this 




Fig. 8. 



A convenient arrangement for mixing Bordeaux mixture. After Vermont 
Agricultural Experiment Station. 



way it will dissolve in a few hours. If it is placed in the 
bottom of a barrel, it will dissolve but slowly, even with 
frequent stirring. When dissolved, the solution may be 
made uniform by stirring. 

A stock solution of lime should be made. Quicklime 
of good quality, which is not at all slaked, should be 
weighed out, placed in a trough, and slaked slowly, using 



28 DISEASES OF ECONOMIC PLANTS 

the minimum quantity of water. Thus a fine quality of 
slaked lime is secured. After the lime is thoroughly 
slaked enough water should be added to make a putty- 
like mass. It should then be covered with more water 
to keep out the air and may be used when needed. Since 
this mass was originally weighed, estimate can be made 
sufficiently accurate to determine the amount of the paste 
to use in any given amount of Bordeaux mixture. 

In preparing the Bordeaux mixture from stock, measure 
out the proper amount of stock solution of copper sulphate, 
dilute it with half of the amount of water needed. In a 
similar way measure out the proper amount of lime from 
the stock and dilute it with the other half of the water in a 
separate vessel. 

The lime should be passed through a fine wire strainer 
of about eighteen meshes to the inch, or through cheese- 
cloth, to remove particles of stone which would other- 
wise cause great difficulty in the pump nozzle when 
spraying. 

The two ingredients are now mixed each with one half 
the amount of water called for in the formula. All 
that remains is to pour them together slowly and stir 
thoroughly. 

It is a matter of considerable importance that the stock 
solutions be diluted before they are mixed with each other, 
since the quality of Bordeaux mixture resulting from this 
method is superior in several respects to that which would 
be made if strong solutions were mixed together and after- 
wards diluted. The Bordeaux should be freshly made 
each time before using. 

An excess of soluble copper compounds in the completed 




IG. 9. — Bordeaux mixture, 1 and 3 properly and 2 and 4 improperly made : 1 and 2 after 
standing 45 minutes : 3 and 4 after standing 4% hours. After Sheldon. 



30 DISEASES OF ECONOMIC PLANTS 

Bordeaux mixture is dangerous to the foliage, while a 
slight excess of lime is a point of safety. It is therefore 
advisable, unless it is certain that sufficient lime of good 
quality is used, to apply a test in this regard. If an excess 
of lime be present in the mixture, the breath expired upon 
it for a few moments, as held in a saucer or cup, will cause 
a flaky film to form upon the surface ; if no such film forms, 
more lime is needed. If an excess of copper sulphate is 
present and a bright piece of iron or steel, a knife blade 
or nail newly filed or sanded, be held in the solution for 
a few moments, a distinct deposit of metallic copper will 
appear upon the bright iron. It is well to practice each 
of these tests with solutions known to have excess of copper 
and lime respectively, to thus become familiar with the 
working of the test. No metal cans or utensils should be 
used in preparing Bordeaux mixture. 

Soda or potash Bordeaux mixture. — While the usual 
lime-Bordeaux mixtures are very successful in preventing 
plant diseases, slight difficulty is sometimes encountered in 
using them, owing to the occurrence of small stones, im- 
perfections in the lime. These, if not thoroughly strained 
out, clog the spraying nozzle and are troublesome. To 
escape this difficulty and to render the preparation and 
application of the Bordeaux mixture easier, as well as to 
give a mixture which can be used as the fruit approaches 
maturity, without spotting it, use of potash or soda as 
a substitute for the lime has been recommended. Soda 
is most acceptable for this purpose. For general use there 
is no indication that these mixtures will supersede the 
ordinary lime-Bordeaux. 



FUNGICIDES 



31 



The Soda Bordeaux 

Copper sulphate (Milestone) ..... 5 pounds 
Commercial caustic soda sufficient to combine with the copper 

sulphate and leave a slight excess of soda. 
Water 50 gallons 

It will be noted that the amount of caustic soda to be 
used is not stated definitely. It is impossible to make a 
definite statement, since the strength of the various com- 
mercial sodas varies greatly. 

The following table gives the amount of copper sulphate 
required for a single can of several of the more common 
sodas. In the last column is found the amount of mixture 
which a can will make. For example, if the Champion 
soda, a can of which weighs 13.75 ounces, is used, one should 
use 1.6 pounds of copper sulphate to each can of soda. 





Gross 
Weight 
op Can 


Weight 

op 

Substance 


Copper 
Sulphate 
required 


Amount 

op 
Mixture 


Soda (Troy) 


11.2 lb. 


10.17 lb. 


46.22 lb. 


462 gal. 


Babbitt's Potash . 


17 oz. 


14.5 oz. 


3 lb. 


30 gal. 


Champion . 


13.75 oz. 


12 oz. 


1.6 lb. 


16 gal. 


Red Seal 


17 oz. 


14.5 oz. 


2.4 lb. 


24 gal. 


Leggett's 


17. oz. 


14.75 oz. 


2.5 lb. 


25 gal. 


Lehman's 


14.75 oz. 


12.25 oz. 


2.4 lb. 


24 gal. 


Hirsh . 


14.5 oz. 


12.75 oz. 


1.8 lb. 


18 gal. 


Washington . 


14.25 oz. 


12.75 oz. 


1.7 lb. 


17 gal. 


Saponifier (Solid) 


15.75 oz. 


14.25 oz. 


2.5 lb. 


25 gal. 


Saponifier (Granu- 










lated) 


17 oz. 


14.75 oz. 


2.6 lb. 


26 gal. 


Natrona 


42.75 oz. 


36.75 oz. 


7.2 lb. 


72 gal. 



32 DISEASES OF ECONOMIC PLANTS 

One can of soda contains 12 ounces of substance and the 
1.6 pounds of copper sulphate together with the one can 
of Champion soda will make 16 gallons of soda Bordeaux. 

In a similar way, by consulting the table, one can find 
how much copper sulphate to use per can with any of these 
brands and how much mixture it will make. 

Dissolve the caustic soda in water. Dissolve the copper 
sulphate also in water in another vessel and dilute each 
solution to half the volume desired in the completed mix- 
ture ; then mix the two solutions together. 

If used in the above proportions, the mixture will be 
alkaline. If too little soda is used, the mixture will be 
acid, and is then liable to injure the leaves. 

The amounts as given in the above table are equivalent 
to the 5-5-50 Bordeaux mixture. If one comparable to 
the 4-4-50 is desired, increase the amount of water by 
25 per cent. 

In order that the mixture may be more easily seen on 
the trees, and thus enable the operator to know when a 
tree has been completely sprayed, a small quantity of 
lime, about one half pound to every 50 gallons of mixture, 
should be added. 

Prepared or dry Bordeaux. — To meet trade demand 
various forms of ready prepared Bordeaux mixture have 
been placed upon the market. While some of these may 
be good, there is no sufficient reason for their use, since 
better and cheaper mixtures can be made at home with 
little or no difficulty. 

Ammoniacal solution of copper carbonate. — This 
solution contains no sediment, and on drying leaves no 
unsightly marks upon the fruit. It may therefore be 



FUNGICIDES 33 

used upon fruits in the latter stages of ripening, when 
the spotting that the Bordeaux mixture causes precludes 
the use of that fungicide. The mixture consists of a 
solution made by dissolving copper carbonate in ammonia- 
water in the following proportions : — 

Copper carbonate 6 ounces 

Ammonia, about 3 pints 

Water 50 gallons 

Weigh out the proper amount of copper carbonate. 
Set a very small portion of this aside, and dissolve the 
remainder of it in diluted ammonia, using only enough 
ammonia to dissolve it. Then add the portion of copper 
carbonate which was reserved. This will insure the use 
of no more ammonia than is necessary. It is better to 
have a little too much of the carbonate in the solution 
than to have too much ammonia. The strong solution 
made in this way can be diluted with the proper amount 
of water. The copper carbonate may be purchased di- 
rectly from the drug-store, or it may be prepared at home. 

To make copper carbonate proceed as follows : Dis- 
solve 10 pounds of copper sulphate in 10 gallons of water. 
Also dissolve 12 pounds of carbonate of soda in the same 
amount of water. Allow these two solutions to cool, 
then mix them slowly together stirring in the meantime. 
Allow the mixture to settle about 12 hours, pour off the 
liquid, and add water equal in amount to the liquid poured 
off. Stir thoroughly and allow it to settle as before. 
Repeat this operation again, then drain off all of the 
liquid possible, and dry the blue powder which remains. 
This powder is the copper carbonate. 

D 



34 DISEASES OF ECONOMIC PLANTS 

Burgundy Mixture. 

Copper sulphate 2 pounds 

Sodium carbonate (sal soda) 3 pounds 

Water 100 gallons 

Each chemical should be dissolved separately in half 
the water, then mixed as in making Bordeaux mixture. 
This mixture may be used as may ammoniacal copper 
carbonate when it is advisable to avoid the spotting of 
fruit which would result from use of the Bordeaux mixture. 

Copper sulphate solution, 1-17. — A solution consist- 
ing merely of copper sulphate and water to kill the spores 
on the bark and supports may be used before the leaves 
appear. 

Copper sulphate 1 pound 

Water 17 gallons 

Dissolve the copper sulphate as in preparing the Bor- 
deaux mixture, dilute it to the required strength, and 
spray upon the trees. The addition of a little lime, one 
half pound to 50 gallons of mixture, enables the operator 
to see exactly what portions of the tree have been sprayed. 

This mixture must not be used after the leaves appear. 

Copper sulphate, 1-7. — Made as above, but using 7 
instead of 17 gallons of water. 

Potassium Sulphide Solution. 

Potassium sulphide (liver of sulphur) ... 1 ounce 
Water 2 to 4 gallons 

This solution should be freshly prepared. It is used 
as a substitute for the Bordeaux mixture, to avoid spotting, 
in the same way that the ammoniacal solution of copper 



FUNGICIDES 35 

carbonate is used, when the fruit has become so large that 
the Bordeaux mixture must be discontinued. Potassium 
sulphide is also especially efficient as a protection against 
the powdery mildews. 

Formalin. — Formalin is a very powerful germicide 
which came into wide use about 1889. Its interest to the 
farmer lies chiefly in its power to prevent the potato scab 
onion smut, and the various smuts of cereals. Full direc- 
tions for its use are given under special crops. 

This substance appears on the market under two names : 
"formalin" and "40 per cent formaldehyde." These 
substances are absolutely identical, and since 40 per cent 
formaldehyde is cheaper, owing to the fact that the word 
" formalin " is protected by patent, the customer will of 
course do well to purchase the 40 per cent formaldehyde. 

Corrosive Sublimate. 

Corrosive sublimate 1 part 

Hydrochloric acid 2 parts 

Water 1000 parts 

This is employed chiefly as a seed disinfectant particu- 
larly for black rot of cabbage. It is intensely poisonous 
and should be so regarded. 

Flowers of sulphur. — This substance is chiefly employed 
as a specific for the powdery mildews. See grape, p. 164. 

Sulphur-S oda -S oap . 

Caustic soda 10 pounds 

Sulphur ........ 35 pounds 

Fish-oil soap 6 pounds 

Water ........ 100 gallons 



36 DISEASES OF ECONOMIC PLANTS 

Bring the soda and a little water to a boil in a kettle, 
then slowly add the sulphur and soap and boil for about 
one hour, with frequent stirring; strain and dilute to 
100 gallons. 

Lime-Sulphur Mixtures 1 

These mixtures are of both fungicidal and insecticidal 
value. 

Home-boiled lime- sulphur wash. — This is the wash 
regularly used against the San Jose scale. 

Lime .20 pounds 

Sulphur 15 pounds 

Water 50 gallons 

The lime, the sulphur, and about half of the water are 
boiled together for forty-five minutes in a kettle over a fire 
or in a barrel or other suitable tank with steam. Strain 
and dilute to 50 gallons and the wash is ready for applica- 
tion. 

For spraying trees in the dormant state this wash may 
be substituted for Bordeaux mixture as a fungicide ; but 
it is injurious to foliage, and cannot be safely used as a 
summer spray unless greatly diluted. 

Factory-boiled or commercial lime-sulphur wash. — 
This solution is practically the same as the home-boiled 
wash and is placed on the market as a substitute for the 
latter. The home-boiled wash is troublesome to make 
and does not keep well. The prepared wash keeps in- 
definitely and is ready for use when received, requiring 
only dilution with water. 

1 Modified from Scott, W. M., IT. S. Dept. Agr. Bur. Plant Indus. 
Circ. 27. 



FUNGICIDES 



37 



For insects and fungous diseases on dormant trees a 
strength of 1 gallon of the solution to 9 to 11 gallons of 
water gives satisfactory results. 

Self-boiled lime-sulphur wash. — The self-boiled lime- 
sulphur wash is a combination of lime and sulphur boiled 



4J,L IP- 




*ii 




H 





Fig. 10. — Making lime-sulphur wash. , After Sherman. 



with only the heat of the slaking lime, and is primarily 
intended for summer spraying as a substitute for Bordeaux 
mixture where the latter is injurious to foliage or fruit. 
For most purposes the Bordeaux mixture is as yet to be 
regarded as the better fungicide and should be used 
except when it is liable to injure the plants. Peach foliage 



38 DISEASES OF ECONOMIC PLANTS 

is so susceptible to spray injury that ordinary Bordeaux 
mixture cannot be used as a summer spray on peach trees ; 
neither can the sulphur washes which contain any consider- 
able quantity of sulphides in solution. The self-boiled 
lime-sulphur wash, however, when prepared as a mechani- 
cal mixture of lime and sulphur with only a small per- 
centage of the sulphur in solution, is not injurious to 
peach foliage and has proved to be a good fungicide. It 
may also serve a good purpose in spraying varieties of 
apples, like the Ben Davis and Jonathan, which are often 
injured by applications of Bordeaux mixture. 

The mixture that appears to be the most satisfactory 
is composed of 

Lime 10 pounds 

Sulphur 10 pounds 

Water 50 gallons 

This can best be prepared in rather large quantities — 20 
pounds, or even 40 pounds at a time — so as to get 
enough heat to produce a violent boiling for a few min- 
utes. Place the lime in a barrel and pour on enough 
water (about 3 gallons to 20 pounds) to start it slaking 
and to keep the sulphur off the bottom of the barrel. 
Then add the sulphur, which should first be worked 
through a sieve to break up the lumps, and finally enough 
water to slake the lime into a paste. Considerable stirring 
is necessary to prevent caking on the bottom. After the 
violent boiling which accompanies the slaking of the lime 
is over, the mixture should be diluted ready for use, or at 
least enough cold water added to stop the cooking; 5 to 
15 minutes, according to whether the lime is quick-acting 



SPRAYING MACHINERY 39 

or sluggish, are required for the process. At the end of 30 
or 40 minutes, if the hot mass is permitted to stand undi- 
luted as a thick paste, a liquid is produced that is dangerous 
to peach foliage and in some cases even to apple foliage. 

The mixture should be strained through a sieve of 20 
meshes to the inch in order to remove the coarse particles 
of lime, but all the sulphur should be worked through the 
strainer. 

Hot water may be used to good advantage in preparing 
the mixture with sluggish lime, but with quick-acting 
lime hot water is not best. If desired, the mixture may 
be kept for a week or more without deterioration, but it 
should be thoroughly stirred before using. 

In applying the self -boiled lime-sulphur wash the spray- 
ing outfit should be equipped with a good agitator. The 
agitator of the ordinary barrel sprayer is not usually 
adequate. 

Combined Bordeaux and Arsenates 

When an insecticide and a fungicide are to be used at 
the same time, it is usually possible to combine the two, 
so that only one application is necessary. 

Bordeaux-Paris-green. — To the usual Bordeaux mix- 
ture Paris green is added at the rate of 5 ounces to each 
50 gallons of mixture. The other arsenical mixtures, as 
London purple, arsenate of lead, or arsenite of lime, may 
also be combined safely with the Bordeaux mixture. 

SPRAYING MACHINERY 

The needs as regards a spraying equipment necessarily 
vary with the amount of spraying to be done, whether a 



40 



DISEASES OF ECONOMIC PLANTS 



small garden or a large commercial orchard. In either 
event proper apparatus is needed. A machine of good 
quality is more durable and cheaper in the end. 

In selecting a pump the fol- 
lowing points 1 should be given 
consideration : — 

1. The air chamber should be 
sufficiently large to ensure a 
steady spray and be so placed on 
the pump that the latter will not 
be rendered top-heavy. 

2. Some means of keeping the 
spraying mixture thoroughly 
stirred is essential. 

3. The working parts should 
all be of brass and be so arranged 
that they can be examined with- 
out undue difficulty. 

4. The pump when mounted 
should not extend above the bar- 
rel more than is necessary. 

5. It is desirable to have the 
device for attaching the pump to 
the barrel so arranged that the 
pump can be readily mounted 

on, or removed from, the barrel. 

6. The different parts of the pump should be so con- 
structed that they can be readily taken apart, especially 
those which inclose the valves. 

7. All points for attachment of the hose should be cut 
with threads of standard size. 




Fig. 11. — Bucket pump showing 
hose, nozzle, and bucket attach- 
ment. After Gould Mfg. Co. 



Modified from the Maryland Agr. Exp. Sta. Rpt. 13, p. 73, 1899. 



SPRAYING MACHINERY 41 

The chief types of pumps are briefly mentioned below. 

Bucket pumps. — These pumps are suited for use in 
the garden ; to spray the bushes or a few small fruit trees 
in the yard. The fact that they may be used in any ordi- 
nary bucket or pail gives them an advantage over some 
of the other outfits. By the attachment of a foot rest which 
extends outside the pail to the ground, the pump can be 
held firmly. They cost from $3 to $7 complete, including 
rubber hose and nozzle. 

Compressed air sprayer. — After the tank is partly filled 
with the spray mixture and closed, air is pumped in, thus 
pressure is exerted upon the liquid, which is forced out in 
the form of a fine spray when the nozzle is opened. 

This type of sprayer is satisfactory in some instances, 
and is adapted to about the same fields as the bucket pump. 
It is not well adapted for spraying large areas, since the 
sprayers are inconvenient to carry, are slow, and heavy. 
They cost from $3 to $7. 

Knapsack sprayers. — These consist of 3 to 5 gallon 
tanks, with straps so attached that the outfit can be carried 
upon the back in the manner of a knapsack. The handle 
is so adjusted that it is operated in front of the carrier. 
These pumps are best adapted to spraying crops which 
grow breast high, as grapes. They may also be used in 
spraying small trees. For general garden use, or small 
areas, a half acre to an acre, they are to be recommended. 
Complete with hose and nozzle, these pumps cost from 
$10 to $20. 

Barrel pump. — For ordinary orchard work the barrel 
sprayer is of most importance. The pump is adjusted to 
a barrel, at either the side or end, preferably the side. It 



42 



DISEASES OF ECONOMIC PLANTS 



should be provided with a good agitator to keep the spray- 
ing mixture stirred while in use. The pump should be 
fitted to carry two leads of hose. Without hose or nozzle 
the cost will be from $13 to $16. 




Fig. 12. — Barrel pump showing agitator. After Gould Mfg. Co. 



Tank sprayers. — These differ from the barrel pumps 
mainly in their larger capacity and mode of obtaining 
pressure. They cost about $25. 

Field sprayers. — This sort of sprayer is used in spray- 
ing low plants, such as strawberries, potatoes, tomatoes, 
cabbage, etc. Several nozzles are attached, so that from 



44 



DISEASES OF ECONOMIC PLANTS 



3 to 6 rows can be treated at one time. Where a number 
of acres of truck crops are grown, this sprayer is of great 
advantage. 

Power sprayer. — Still larger sprayers, either geared to 
wheels to use horse power, or operated by steam or gasoline, 
are used by the large commercial growers. 




Fig. 14. — Sulphuring machine in use. After Faurot. 



Nozzles. — The nozzle should be one that will throw 
the liquid into a very fine spray, a mist. From the Ver- 
morel the liquid issues in the form of a cone-shaped mist. 
From the Bordeaux nozzle it issues in a fan-shaped spray 
which is not so fine as that given by the Vermorel type. 
The Bordeaux nozzle may be used to better advantage to 
spray tall trees. 

Sulphuring and dusting machines. — These consist of 
various forms of bellows or blowers driven by hand or 



COST OF SPRAYING 



45 



other power. The points to be desired are evenness of 
flow, economy of sulphur, and ease of operation. The 
discharge of the sulphur from the exit is shown in Fig. 14. 



COST OF SPRAYING 

Since both the cost of labor and of materials vary, and 
the amount of each required is determined by the size 
of the plants to be sprayed, no accurate estimate of the 









" "^.Jf '1 








-' f->£ 








■-M 








'JA 




1 








_ .,,/VV 




.. 


> 






'■. -■-.■". ,■' 








':'.-■■ t ■&"''" 


" m %>" 








■ -,. • '■HI^PJi^Mi 


• • 






ys& 


';. ,,;»., ,■■ ,■:■:.-.';■■■ 





Fig. 15. 



The nozzles are turned at an angle to the rod so that the spray may be 
directed upward or downward. After Faurot. 



cost of spraying can be given. Still reasonably reliable 
estimates may be made from the following examples. 

Orton 1 estimates the cost of spraying cucumbers or 
cantaloupes as follows: '"On the average, 15 acres per 

1 Orton, W. A., U. S. Dept. Agr. Farmers' Bui. 231, p. 22. 



46 DISEASES OF ECONOMIC PLANTS 

day were sprayed, making the labor cost 33 cents per acre. 
Assuming that 100 gallons per acre were applied, the total 
would be : — 

Copper sulphate, 6 pounds at 7 cents per pound . . $ .42 

Lime, 12 pounds at 1 cent per pound .... .12 

Total cost of material $ .54 

Total cost of labor . . . . . . . . .33 

Cost per acre of each application . . . . ' . $ .87 

Cost per acre of six applications . . . : . . 5.22 

"There should be added for interest on investment, 
repairs, and depreciation of outfit, $1 per acre, which 
increases the total cost to $6.22 per acre." 

Spraying potatoes, tomatoes, or any other crop which 
in like manner covers the ground costs approximately the 
same. 

" The cost of treating pear, plum, and cherry stock the 
first year, or before and after the buds are inserted, will be 
about 25 cents for 1000 trees. The next year, or when the 
buds are making their first season's growth, the cost of the 
work will probably not exceed 25 cents, while the following 
season or the second year from the bud, the cost will be 
increased 10 to 15 cents, or about 40 cents per thousand. 
On this basis the entire cost of treating trees until they are 
two years old from the bud will range from $.85 to $1 per 
thousand, or about 1 mill per tree." 1 

At Southern Pines, N.C., a careful account was kept 
of the cost of treating grapes, including both material and 
labor. The Bordeaux mixture cost almost exactly 50 
cents a barrel. The labor was estimated as the work of 

1 U. S. Dept. Agr. Div. Veg. Physiol. & Path. Bui. 7, p. 27. 



COST OF SPRAYING 



47 



three men, each at $1 per day. The following table gives 
the cost per acre of the material and labor for each of the 
6 sprayings : — 



Spraying 


Cost of 
Material 


Cost of 
Labor 


Total Cost 
per Acre 


1st 


$ .45 


$1.13 


$1.58 


2d 








.68 


1.13 


1.81 


3d 








.68 


1.10 


1.88 


4th 








1.36 


1.47 


2.83 


5th 








2.06 


1.65 


3.71 


6th 








2.06 


1.65 


3.71 


Total 


$7.39 


$8.13 


$15.52 



For potatoes " the items of expense of spraying 10.4 
acres five times were as follows : — 



234 pounds copper sulphate at 7 cents 

195 pounds prepared lime at 11 cents 

90 quarts arsenite of soda solution at 2\ cents 

70 hours labor for man and horse at 30 cents 

Wear on sprayer 

Total 



$16.38 

2.92 

2.10 

21.00 

6.50 

$48.90 



"The total expense of spraying was $4.70 per acre or 94 
cents per acre for each application." 1 

According to Kinney 2 the cost of spraying apple trees 
twice with combined Bordeaux mixture and Paris green, 
and once with Bordeaux mixture, has been estimated as fol- 



1 Stewart, F. C. 
p. 257. 

2 Kinney, L. F., 



and others, N. Y. (Geneva) Agr. Exp. Sta. Bui. 290, 
R. I. Agr. Exp. Sta. Bui. 31, p. 15. 



48 



DISEASES OF ECONOMIC PLANTS 



lows by Mr. George W. Burlingame who had charge of the 
work : — 

466 gallons of Bordeaux mixture $9.68 

11 pounds of Paris green .45 

Labor of 3 men, preparing and applying the mixture 60 hours 9.00 

Use of team 20 hours 3.00 

Total 22.13 

This amount when divided among the 131 trees treated 
makes the cost of the treatment 16.9 cents per tree. 

The cost of spraying in Missouri x is reported as follows : 
Arsenate of lead estimated at 12 cents per pound, blue 
vitriol at 6J cents, and lime at \ cent. In computing the 
cost of applying the sprays, $5.75 per day was taken as 
a liberal estimate for labor of team and three men and 
for gasoline and oil required to operate the power outfit. 
This placed the wages of each man at $1.25 per day. 

Cost of Spraying Ingram Apples in Missouri 





>> 




X 


h% 


■k 


"o a 


°al 




2 


£n~ 


as 


g.a_ 


a^ 


4j 03 t,^ 


■S rt a 






OJ 01 O) 


~ — 

a® 

■r. a 




ri 3 <u 

's.'Ss 

_ = - 

K fi O 

gaift 
a.S 


ed cos 
al and 
tion p« 
(cents 


OT3 !h 
O (- o> 

£"3 a 




C o> 

_o a 
"3 




o u 


abc-p 


rnbin 
ateri 
plica 
tree 


•S-C.2 




O 




o 
O 


H - 


H 


° S 


as--E 


1st spray . 


. 4.74 


4.9 


$3.19 


3.86 


$2.51 


8.76 


$5.70 


2d spray . 


. 3.67 


2.2 


1.43 


1.85 


1.20 


4.05 


2.63 


3d spray . 


. 3.44 


2.0 


1.30 


2.06 


1.34 


4.06 


2.64 


All sprays . 


. 11.85 


9.1 


5.92 


7.77 


5.05 


16.87 


10.97 



1 Taylor, E. P., Mo. State Fruit. Exp. Sta. Bui. 21, p. 40, October, 
1909. 



COST OF SPRAYING 



49 



Spraying at Avon, Va., during the Season of 1905, and 
its results 1 



Plot 


Ntjm- 


Treatment with Bordeaux Mixture 
(5-5-50 Formula) 


Picked Sept. 19 to 23 


BERS (2 

Trees to 
Each Plot) 


00 

a 
< 


>> 


OS 
>> 


3 


i> 

<N 

Oi 
PI 

1-5 


o 

>> 

3 

1-3 


U5 


si 
< 


< 


a 

(72 


Sound 
Fruit 


Rotten 
Fruit 


Per- 
cent- 
age of 
Sound 
Fruit 
























Bushels 


Bushels 




1 . . . . 


n 


" 


" 
















18.50 


30.25 


37.9 


2 . 






" 


" 


" 


" 


" 












47.50 


22.50 


67.8 


3 . 






" 


" 


" 




" 


II 


a 


— 


— 


— 


56.00 


2.00 


96.5 


4 . 






" 


" 


" 




" 


" 


" 


" 


— 


— 


54.00 


1.75 


96.8 


5 . 






a 


" 


" 


ii 


II 


" 


" 


a 


" 


— 


32.75 


1.15 


96.6 


6 . 






a 


" 


" 


" 


" 


" 


" 


a 


" 


" 


68.50 


.70 


98.9 


A. 






Checl 


— one untr( 


jatec 


tree 




.00 


10.00 


00.02 


7 . 






" 


" 




— 








" 


// | // 


" 


56.50 


14.00 


80.1 


8 . 






" 


" 




— 








— 


" " 


ii 


7.00 


6.50 


51.8 


9 . 






— 







— 


" 


" 


" 


— " 


— 


28.50 


6.00 


82.6 


B 






Checl, 


: — one untreated tree 




.00 


17.00 


00.0 2 


10 






— 1 — 




— \ " \ " 


a 


// // 


" 


59.00 


6.50 


90.0 


11 






— — 




// 


a 


// // 


" 


42.25 


6.50 


86.6 


12 






— | — 




— 1 — — 


" 


// // 


n 


28.50 


24.75 


53.5 


C 






Checl, 


: — one untreated tree 




.00 


13.00 


00.0 


D 






Check — one untreated tree 




.01) 


20.75 


00.0 2 


15 






— 1 — 






" 


a i // 


ii 





52.25 


5.25 


90.8 


16 






— — 




— 


II II 


// // 


— 





52.50 


3.75 


93.3 


17 






— 1 — 




" 


II II 


" — 


— 





40.00 


5.00 


88.8 


E 






Check — one untreated tree. 




.25 


16.25 


1.5 



In Arkansas 400 gallons of mixture were required for 
one spraying of 200 trees, and the work was accomplished 
with four men and one team in one half day. The 40 
pounds of bluestone at 8 cents a pound cost $3.20 and the 
same amount of lime at one half cent a pound cost 20 
cents. The four men, at $1.25 a day each, cost for the 
half day $2.50, and the team cost $1 for the half day. 
This aggregates $6.90 for spraying 200 trees, or a little less 
than 3J cents a tree for the one application, making a total 

1 Scott, W. M., U. S. Dept. Agr. Bur. Plant Indus. Bui. 93, p. 23. 

2 Of the check trees, A had 1 sound apple, B 6, and D 2, but the per- 
centages were too small to show in the table. 

E 



50 DISEASES OF ECONOMIC PLANTS 

cost of 10|- cents a tree for three applications. This is the 
cost of the bitter-rot treatment alone ; if the cost of the 
arsenate of lead used for protection against the codling 
moth be included, 1^ cents a tree for each application should 
be added. 1 

PROFITS FROM SPRAYING 

Spraying protects the foliage and harvest from insect 
and fungous attacks. — By properly spraying, perfect 
produce and good yield are often obtained where the 
omission of spraying would mean poor yield and diseased 
products, or permanent injury to the plant in the case of 
perennials. 

A marked increase in yield is often evident to even a 
casual observer. To accurately judge this value in first 
experiences some portion of the crop should be left un- 
sprayed, and the yield from sprayed and unsprayed parts 
should be carefully measured and the gain compared with 
the cost of treatment. In the conduction of any large 
business every small increase in profit and every saving 
of leakage is important. 

Perfection of produce. — The quality as well as quantity 
of the yield is improved by spraying. The perfect product 
proves its excellence on the market by its ready sale and 
the high price it commands. 

One cannot afford to raise inferior produce. The in- 
crease in quality, even if the quantity of the yield were 
not affected, is sufficient reason for spraying. The keep- 

1 Scott, W. M., and Quaintance, A. L., U. S. Dept. Agr. Farmers' Bui. 
283, p. 13 ; April 29, 1907. 



PROFITS FROM SPRAYING 



51 



ing quality of many kinds of produce is increased by 
spraying. 

Protection of the plant. — In many cases the benefits 
are apparent the second and succeeding rather than the 




Fig. 16. — Potato field showing benefits of spraying. Portion at left received 
Bordeaux mixture and Paris green ; portion at right received Paris green only. 
Original. 

first year, since spraying protects the foliage, the func- 
tion of which is to accumulate nourishment for the crop 
of the following year. 

Spraying should be regarded as insurance. It pro- 
tects the crop against the devastation of disease, yet in 
most cases it differs from insurance in the fact that it 



52 DISEASES OF ECONOMIC PLANTS 

pays for itself year by year even if there be no general 
epidemic. 

A few quotations from various sources to illustrate the 
benefits of spraying are appended. 

" The return per acre from unsprayed area (grapes) is 
calculated at 316 baskets per acre, worth less than $10 per 
acre, while from the sprayed areas the average yield was 
1252 baskets per acre, worth $125.20 per acre, secured at a 
cost of $7.50 per acre." — Ohio Bulletin, 130, p. 46. 

In New York (Geneva) in one case spraying for pear 
scab at a total cost of 55 cents per tree increased the aver- 
age yield from 45 cents to $6.55 per tree, a net profit of 
$6.10 per tree. 

From records concerning plum spraying it appears that 
where the trees were sprayed, the average per tree of picked 
fruit was increased 44 per cent, the marketable drops in- 
creased 8 per cent, and the waste decreased 81 per cent. 
The total yield of marketable fruit as recorded in pounds 
was 45 per cent greater where the trees were sprayed than 
where they were not sprayed. 

In experiments at Tryon, N.C., the average weight of 
good grapes obtained from a vine in the unsprayed rows 
was 1 pound 1.5 ounces, as compared with 4 pounds 5.8 
ounces from those given 6 sprajdngs with normal Bordeaux 
mixture, a difference of 4 pounds 4.3 ounces to the vine, 
or over a ton to the acre. This gain of a ton or more of 
grapes to the acre was due entirely to the 6 sprayings, at a 
cost of $15.42. 

The following table shows the results obtained with 
potatoes in the volunteer experiments in New York during 
the past five years, 1904-1908 inclusive : — 



PROFITS FROM SPRAYING 



53 



Table 1 showing Results of Volunteer Experiments, 
1904-1908 



Year 


Number of 
experiments 


Total area 
sprayed 


Average gain 

per acre due to 

spraying 


Average market 

price per bushel 

of potatoes at 

digging time 


1904 . . . 

1905 . . . 

1906 . . . 

1907 . . . 

1908 . . . 


41 
50 
62 
24 
11 


A. 

364 
407 
598 
264 

74 


Bu. Lbs. 

58 28 

59 32 
53 6 
30 28 
66 18 


Cts. 

43.5 
57.0 
44.5 
58.0 
66.0 



Average gain for 5 years (188 experiments) 50£- bushels per acre. 

Thoroughness in spraying. — Unless thoroughly and 
carefully done the results from spraying may be disap- 
pointing. Spraying is an operation that requires careful 
heed to directions, and painstaking, patient execution. 
Poorly done, the benefits may be nil or damage may result 
from the chemicals applied. Failures to get good results 
from spraying, in the large majority of cases, have been due 
to lack of thoroughness on the part of the operator. By 
thoroughness it is meant that every part of the plant sur- 
face is to be coated with a film of the spraying mixture. 
Failure to do this leaves some points vulnerable. On the 
other hand too large an application of fungicide is unde- 
sirable, often resulting in injury and death of the green 
part, and always leading to waste of fungicide. When 
the fungicide accumulates in drops and drips or runs off, 
too much is present. To apply so little that none drips, 

1 Stewart, F. C, and others, N. Y. (Geneva) Agr. Exp. Sta. Bui. 311. 



54 DISEASES OF ECONOMIC PLANTS 

yet so much that all the surface is coated, is the aim. This 
necessitates a good nozzle giving a spray, or mist, and not 
drops. It implies also intelligent care and close attention 
to all the details of the operation. 

SOIL DISINFECTION 

Soil disinfection in the field has as yet in the main 
proved impracticable. All promising chemicals have been 
tried without avail. Electricity has not given beneficial 
results, and at present there is no hope of any practicable 
manner of ridding fields of parasites by any process of 
disinfection. In a few instances large applications of lime, 
formalin, or sulphur have proved beneficial (see sweet 
potato, onion, etc.), but the general practicability of such 
usage is doubtful. 

Disinfection of limited areas is, however, practicable, 
is largely employed, and has already resulted in great 
benefit. Cutting benches, flats, and other benches in the 
greenhouse, cold frames, and seed beds, and other small 
areas may be disinfected with advantage. The means to 
be employed depend upon the area, its location, and the 
facilities at hand. The leading methods are given below : — 

Baking. — Flats, pots, and other small containers of 
earth may often be satisfactorily disinfected by placing 
them for some time upon the boiler or over a stove, or in 
an oven for a comparatively long period. 

Permanent steam disinfectors. 1 — A system of lj- 
inch pipes, which are perforated with ^-inch holes on their 

1 Adapted from Gilbert, W. W., U. S. Dept. Agr. Bur. Plant Indus. 
Bui. 158, October, 1909. 



SOIL DISINFECTION 55 

under side at intervals of 6 inches throughout their entire 
length, may be placed about one foot below the surface 
of the soil. The pipes should run lengthwise of the bed, 
18 inches apart, and be connected with a steam boiler 
capable of producing 80 to 100 pounds' pressure. Before 
treatment the soil should be thoroughly spaded up and 
pulverized to permit ready access of the steam to all parts, 
and all fertilizers except commercial ones should be ap- 
plied at this time, since fresh spores of the fungus might 
be carried in if manure were added after disinfection. 

The bed to be treated should be covered with several 
thicknesses of old burlap or blankets to confine the heat 
to the soil. The steam should be applied at a pressure 
of 80 to 100 pounds, since at high pressure it is much drier 
and the soil is not wet as much as when low-pressure steam 
is used. A treatment of from one to two hours is usually 
sufficient thoroughly to disinfect the soil to a depth of 18 
inches. A few potatoes laid in the surface soil will indicate 
the thoroughness of the treatment by the degree to which 
they are cooked. The blankets might advantageously 
be left on for some time. 

While this method offers some advantages for seed beds 
of limited area, in that the pipes may be left in the ground 
and used year after year with little extra labor and may 
also be used for subirrigation, the initial cost of installa- 
tion, especially on large seed-bed areas, may be prohibitive. 

Inverted-pan method. — The method which has given 
the best results in practice, and which because of its simplic- 
ity and small cost recommends itself for use on large or 
small areas, is the invention of Mr. A. D. Shamel, of the 
U. S. Dept. Agr. Bur. of Plant Industry, and was devised 



56 



DISEASES OF ECONOMIC PLANTS 



by him to disinfect nematocle-infested soils in Florida. 
The apparatus consists of a galvanized iron pan, 6 by 10 
feet and 6 inches deep, which is inverted over the soil to 
be disinfected, and the steam admitted under pressure. 




Fig. 17. — Disinfecting with steam by the inverted pan method. After Gilbert. 

The pan is supplied with steam-hose connections, has sharp 
edges, which are forced into the soil on all sides to prevent 
the escape of steam, and is fitted with handles for moving 
it from place to place, the weight of the entire pan being 
not over 400 pounds. 

The soil is prepared as in the greenhouse method, a few 
potatoes being buried at a depth of a foot to gauge the 
degree of heat attained, or a soil thermometer may be 



SOIL DISINFECTION 



57 



used if desired. The steam should be kept at as high a 
pressure as possible, 80 to 100 pounds being best, and the 
treatment should continue for one or two hours, depending 
on the pressure maintained. In experiments conducted 
on tobacco seed beds in the spring of 1907, one hour's 
steaming at 80° C. gave best results in killing both the fungi 




Fig. 18. — Disinfecting soil with a Sargent disinfector. Original. 



and the weed seeds. When one section of the bed is 
treated, the pan is lifted and carried to another portion, and 
the operation repeated until the entire bed is steamed. 

The Sargent method. — Disinfection by a system of 
steam pipes arranged in the form of a harrow, with hollow, 
perforated teeth, has proved satisfactory under some 
conditions. 

Surface firing. — Surface firing of seed beds has been a 
common practice for years in some tobacco sections, par- 



58 DISEASES OF ECONOMIC PLANTS 

ticularly Kentucky and other Southern States, the end in 
view being the improvement of the tilth of the soil and the 
killing of weed seeds rather than of any fungous diseases. 
In Italy, as well, burning is now considered a part of the 
regular method of tobacco seed-bed preparation, it having 
been resorted to as a preventive of Thielaviose. 

Two methods of surface firing are in vogue; the first 
by direct firing, the second requiring the use of a pan. In 
the direct method, the land to be disinfected is first 
thoroughly pulverized and manure applied. It is then 
covered with straw, brush, and wood sufficient to make a 
hot fire. This is ignited and allowed to burn an hour or 
so. The ashes are raked into the surface soil, and the seed 
is sown. 

The second method, pan firing, consists in the use of a 
sheet-iron pan, 3 by 9 feet, under which a fire is made. 
This is set in the middle of a 9-foot bed, and the soil on 
one side to a depth of 6 inches is shoveled in and heated, 
great care being taken to keep it moist, otherwise the 
humus would be burned out and the physical texture irrepa- 
rably altered. After an hour this soil is put back and 
that from the other side of the pan subjected to the same 
treatment, and then, the pan moved along to a new place. 
The soil underneath the pan itself is thereby subjected to 
heat for two hours. 

Formalin disinfection. — The use of formalin for the 
disinfection of greenhouse soil and of tobacco seed beds 
against Rhizoctonia has been in vogue for some time with 
excellent results. It furnishes a very simple means of 
disinfection as follows : The beds are thoroughly prepared 
as for the other methods of disinfection described and are 



SOIL DISINFECTION 59 

then drenched with a formalin solution composed of one 
part of commercial formalin (40 per cent formaldehyde) to 
150 to 200 parts of water, three fourths to one gallon of 
this solution being used to the square foot of bed space. 
The solution should be put on with a watering pot with a 
rose and distributed as evenly as possible over the bed, so 
as thoroughly to wet the soil to the depth of a foot. It will 
in most cases be necessary to put this solution on in two or 
three applications, as the soil will not take in this quantity of 
water immediately. The beds should then be covered with 
heavy burlap or a tarpaulin to retain the fumes for a day 
or so, and then aired for a week before sowing the seed. 

Spring applications of formalin are open to the following 
objections : The addition of such a large quantity of water 
to the soil keeps it wet and cold longer than would naturally 
be the case, thus delaying germination as well as subsequent 
growth; the necessity of airing the beds to remove the 
formalin fumes and to allow the soil to dry out also causes 
delay in seeding. To obviate these difficulties the beds 
should be treated in the fall, before freezing. In this case a 
stronger solution, 1 to 100, may well be used, as there will 
then be no danger of injuring the seedlings. 



GENERAL DISEASES 

The causal fungi of the diseases discussed below are 
found upon so many different kinds of plants that it would 
seem that they are often indifferent as to the nature of 
their hosts. They may, therefore, be expected upon 
almost any kind of plant, and are here mentioned so that 
it will not be necessary to refer to them repeatedly in suc- 
ceeding pages. Especial reference is also made to them 
under the hosts to which they are most destructive. 

Damping off. — Seedlings, cuttings, and other weak, soft 
plants which lack in the vigor that affords them natural 
protection against their enemies, are subject to a disease 
which has come to be generally known to gardeners as 
" damping off." Damping off is most injurious to seedlings 
grown indoors or under crowded conditions, but it some- 
times occurs in the field. Tj^pically it occurs upon seedlings 
as a rot originating at or near the surface of the ground. 
The decay at this point so weakens the stem that the 
plant topples over or " damps off." Subsequently the 
whole plant may decay, either from the primary cause or 
from secondary attacks. A short time prior to the fall of 
the plant the leaves may appear sickly, although this sign 
is so evanescent that it may not be noted. 

Upon cuttings the toppling over does not, of course, occur, 
but the rot at the ground line is of the same nature as in 
the case of seedlings, and since the diseases in the two cases 

60 



GENERAL DISEASES 61 

are of similar nature and due to similar causes, they are 
placed under the same caption. 

Damping off may be caused by any one of several species 
of fungi, prominent among them being Pythium, Rhizoc- 
tonia, Botrytis, Sclerotinia, Phoma, Volutella, Phytoph- 
thora, Colletotrichum, Glceosporium. The fungus which 
causes this condition may often be seen as a weft of myce- 
lium around the base of the diseased plant, or even creeping 
over the ground to some distance. From its original 
points of attack it may spread rapidly to adjacent plants, 
often sweeping the whole seed bed. 

Since the growth of these fungi is favored by moisture 
and warmth, the trouble may often be checked or pre- 
vented by keeping the beds cool and withholding any excess 
of water ; also by means of adequate ventilation, preventing 
the accumulation of a vapor-laden atmosphere around the 
bases of the plants. Frequent stirring of the top soil 
around the plants aids in drying it and may stop an in- 
cipient attack of damping off. 

Organic matter in the soil favors the growth of damping- 
off fungi, and should be avoided. Fresh, clean sand is best 
for most purposes of the seed bed and cutting bench. 

Soil known to have once sustained damping off may be 
regarded as infected with a fungus which caused it. Such 
soils should not be used for seedlings or cuttings without 
disinfection. If disinfection is impracticable, the soil 
should be removed, the containers thoroughly disinfected 
with a spray of Bordeaux, bluestone, or formalin, and new 
uninfected soil introduced. 

Rhizoctoniose (Rhizoctonia) . — In America this dis- 
ease is known to affect potato, beet, cotton, lettuce, bean, 



62 DISEASES OF ECONOMIC PLANTS 

currant, celery, radish, rhubarb, Asparagus Sprengeri, 
aster, carnation, sweet william, coreopsis, violet, cherry, 
pine, cucumber, begonia, coleus, verbena, hydrangea, 
candytuft, sage, phlox, pyrethrum, snapdragon, raspberry, 
lambs'-quarters, tumble-weed, pigweed, and squash, while 
in Europe it is known upon many more species of plants. 
If conditions favorable to its attack obtain, the fungus may 
well be expected upon almost any species of plant, so wide 
is its range of hosts. For complete description see potato, 
p. 271. 

Soil disinfection, when practicable, may be employed; 
otherwise general sanitary measures, destruction of infec- 
tive refuse, and the use of resistant plants are remedial. 

Sclerotiose (Sclerotium Rolf six Sacc). — The chief symp- 
toms of this disease, with treatment, are described under 
pepper, p. 259. The causal fungus seems almost omnivorous, 
and may be recognized upon numerous hosts in the southern- 
most states. It has been identified upon tomato, eggplant, 
Irish, potato, sweet potato, beet, peanut, bean, cowpea, cab- 
bage, squash, watermelon, rhubarb, fig, cotton, violet, 
hydrangea, daphne, chrysanthemum, cantaloupe, morning- 
glory, carrot, Japanese fiber plant, grasses, o&ulinower, 
sugar cane, and several weeds. 

Texas root rot, Ozoniose. — Most destructive to cotton 
under the name of the Texas root rot (see p. 401) this 
disease affects a very wide range of plants in regions 
where the causal fungus exists. The disease has been re- 
ported from Texas, Oklahoma, New Mexico, and Arizona. 
It has been noted upon nursery stock (except Prunus), 
apple, mulberry, china berry, persimmon, elm, lime, maple, 
Sida spinosa, ragweed, cocklebur, and alfalfa, 



GENERAL DISEASES 63 

Soil diseases. — A type of plant disease of special de- 
structiveness comprises those of which the causal organism 
resides in the soil from year to year ready to infect any 
susceptible crop planted thereon. 

Notorious among such are the wilts of the cotton, tobacco, 
cowpea, watermelon, flax, and potato; the club root of 
cabbage and other crucifers; black rot of similar plants; 
smut of onion; Texas root rot. Other soil diseases are 
wilt of tomato, cucumber, cantaloupe, eggplant, potato 
rosette and scab, beet scab, lettuce drop, and numerous 
others mentioned on following pages. Since all of these 
are to large extent similar in propagation and dissemination, 
they are given general treatment here. 

The particular destructiveness of these diseases is due 
to the fact that they not only kill the crop, but they 
also prohibit successful culture of susceptible crops in suc- 
ceeding years. This crop limitation, if the crop in ques- 
tion be an important one, perhaps the only really profitable 
one suited to the soil affected, may result in large depre- 
ciation in land values. 

It is unknown how long the germs can live in the soil 
without their favorite host plant. That they can live from 
one season to the second season following is certain. A 
field slightly affected one year, if put to a susceptible crop 
the second year after will be even more seriously diseased, 
and the trouble will grow so long as susceptible crops are 
cultivated with but short intervening periods. Many 
cases are known where a rest of five and even eight years 
does not materially restore the soil to health. 

The application of chemicals to the soil is of value only 
in rare instances, and is even then questionable. No 



GENERAL DISEASES 65 

means of soil disinfection applicable to fields is known. 
Land once infected can therefore become again usable only 
by eliminating the causal organisms by a long system of 
rotation which is usually only partially effective, or by the 
use of resistant varieties of plants, and these in most in- 
stances are not yet known. 

In view of these facts it is especially necessary to stress 
the importance of protection of healthy soils against these 
diseases. To understand the means of protection the 
modes of dissemination must be known. 

All plants affected with these diseases harbor immense 
numbers of the reproductive parts of the causal organisms, 
bacteria, spores, mycelium, etc. Upon the death and dis- 
integration of the host plant they are liberated in the soil, 
where they are able to live for considerable time. The 
immensity of their number in a diseased plant is incon- 
ceivable. Even a few diseased stems, roots, or leaves in 
the field will stock the soil thoroughly with them. In- 
fected plants, or soil in which infected plants have been, or 
which bears parts of infected plants, can therefore convey 
such diseases to healthy fields. 

Instances may be cited where the contagion has spread 
by washing from higher land to lower; so, too, may it be 
carried by any means which can convey soil from a sick 
to a healthy field, notably through tools, which have been 
used on diseased soil. Though apparently clean, such tools, 
if they bear even minute particles of infected soil, may 
convey hundreds of germs and thus start an epidemic in 
an uninfected field. The hoofs of animals or the feet of 
laborers may in a similar way bear disease-laden soil. 
Wind passing over an infected field may pick up broken 



66 DISEASES OF ECONOMIC PLANTS 

bits of sick plants or germ-laden soil, and convey these to 
healthy fields. Infection by wind, however, seems to be 
rare, possibly because of the germicidal action of the sun's 
rays upon the surface layer of soil upon which the wind 
must act. If the crop be one which is used for stock feed 
or one which may become mixed with stock feed, the dis- 
ease may be spread widely through manure which has here 
become infected from the feed (cf. watermelon, cabbage). 

A field now healthy may be protected from higher land 
that is infected by proper arrangement of dykes. In some 
cases a thorough cleansing of tools so that there is no pos- 
sibility of conveying the germs will aid in repression. 
The dirt may be knocked off, then wiped off, and the 
implement finally disinfected with a solution of 2 per cent 
formalin or 5 per cent carbolic acid. It is difficult to 
insure complete protection against disease dissemination 
by the feet of animals and man, but if uninfected land 
remains to be protected, every precaution should be exer- 
cised in this particular. 

Where but a few plants in a field are affected, they should 
be removed from the soil and destroyed by fire, — root, 
branch, and leaf. Prompt action here may materially 
lessen the rapidity of spread of the disease in the field. 
Every particle of the sick plant burned means the destruc- 
tion of millions of the causal organisms. 

A long rotation of crops, one that will bring the suscep- 
tible plant back upon the affected field only after an inter- 
vening period of several years, perhaps after a period of 
eight or ten years, is useful in some cases, notably with 
potato wilt, though in other cases, notably watermelon 
wilt, such rotation is of little avail. 



GENERAL DISEASES 



67 



The one means of overcoming these soil diseases which 
is most promising to farmers who own affected soil lies in 
the discovery of a variety of the crop plant that will not 





' 


\ I 


* **%* ; i» 


%r ^^Tj^ 


I iM^i'^. ' "•'' " ^ 




0- T &£' « 




v ' '. 



Fig. 20. — Root knot (nematode) on salsify. Original. 



succumb to attack even when planted upon sick soil. 
Varieties of cotton that can resist the cotton wilt, of flax 
that can resist flax wilt, and of cowpeas that can resist 
the cowpea wilt have been discovered. There is similar 
hope in regard to other crops. 

Root knot, Nematode galls. — Root galls, varying from 
a few millimeters to a centimeter or more in size and super- 



68 DISEASES OF ECONOMIC PLANTS 

ficially resembling the root tubercles of the legumes, are 
common upon a large variety of crops and, though they 
do not properly fall within the province of this book, a 
word is due to them on account of their extreme destruc- 
tiveness. They are due to a microscopic worm which enters 
the root from the soil and by irritation of the root causes 
the gall to develop. Soil infected with these worms will 
produce disease symptoms upon susceptible crops, and con- 
siderable diminution in the vigor of the plant results. The 
cotton, cowpea, watermelon, and tobacco are especially 
susceptible, though the list to include all susceptible species 
would extend into the hundreds, including many prominent 
ornamentals. The only remedies are those suggested 
under soil diseases, with especial stress upon crop rotation 
and the use of resistant varieties. 



DISEASES OF SPECIAL CROPS 
Pomaceous Fruits 



APPLE 



Bitter rot, ripe rot (Glomerella rufomaculans (Berk.) 
Spaul. & von Schrenk). Untrue to its two common names, 
this malady does not always render apples bitter, though 




Fig. 21. — Apple bitter rot (glomerellose) in early stage showing pycnidia. 
After Scott. 

this is sometimes the case ; nor is the disease always lim- 
ited to ripe fruit. Its effect is seen upon both the fruit 
and the twig. 

Upon the fruit it produces a soft, wet, or in later stages 
corky, more or less dry, brown, tan-colored, or black, 

69 



70 



DISEASES OF ECONOMIC PLANTS 



circular, rotten spot. This spot under favorable conditions 
rapidly increases in diameter, the rate varying from 1-10 
mm. each day. The spots may be either single upon the 
fruit or very numerous, depending upon the abundance of 
the infecting spores. When a spot becomes quite large, it 
is usually somewhat depressed, with a shriveled, wrinkled 

surface, due to loss of 
turgor of the under- 
lying tissue caused by 
evaporation. As the 
spot ages minute spor- 
ing pustules of the 
causal fungus, barely 
visible to the naked 
eye, appear, first at or 
near to its center. The 
tissue of the fruit is 
affected to some depth, 
although the progress 
of the disease is not so 
rapid downward as lat- 
erally. The pulp of the 
apple at the margin of the rotten region is usually bitter, 
thus giving rise to one of the common names of the 
disease. 

Fruit of any age after its formation is liable to infection 
if suitable climatic conditions and infective material obtain, 
though the disease is most noticeable and does most dam- 
age as the fruit approaches maturity. A series of hot, 
wet days favors a destructive attack, while cold checks 
it. The fruit as soon as it is badly rotted usually falls 




Fig. 22. 



— Apple in advanced stage of bitter rot 
(glomerellose). After Scott. 



DISEASES OF SPECIAL CROPS 



71 



from the tree, covering the ground beneath, while apples 
less advanced in disease still hang upon the limbs. 




Fig. 23. — Bitter rot canker formed where a limb was broken. After Burrill. 

This same disease affects twigs and young branches, 
causing cankers or rough spots on the bark, which (Figs. 23, 



72 DISEASES OF ECONOMIC PLANTS 

24) vary in size according to their age, persisting and enlarg- 
ing year after year. Young cankers are slightly rough, owing 
to the dead bark, and extend only partly around the twigs. 
Old cankers are very rough, and may extend several centi- 
meters longitudinally along the twig, thus giving it a flat- 
tened appearance. 

The fungus causing the rot upon the fruit was described 
in 1856 by Berkeley. That the cankers are caused by the 
same fungus was recognized independently by two research 
parties, Burrill and Blair, and von Schrenk and Spaulding 
in 1902. Upon both twigs and fruit the spores are borne 
in great numbers. The fungus is, moreover, perennial 
upon the twigs, the cankers serving as initial points of in- 
fection for each year's epidemic. 

The natural course of the disease is thorough twig infec- 
tion; spores from some older lesion are transferred to 
points of weakness on the twig, such as ruptured bark due 
to any cause. The fungus here grows rapidly, produces 
a canker, and forms many spores. These in turn, carried 
chiefly by rain, partly by insects, wind, or other agencies, 
reach other susceptible twigs and cause other cankers or 
fall upon apples, and there initiate spots of rot. Apples 
thus infected serve as multiplying ground for the further 
infection of other apples, thus giving rise to the chief part 
of the fruit rot. Six days after an apple is infected a crop 
of spores may mature and be ready to further spread the 
disease. To some extent the causal fungus hibernates in 
mummified fruits, which thus become sources of initial 
infection for the succeeding year. 

Bitter rot occurs throughout the United States wherever 
apples grow, but has been most destructive heretofore in 



DISEASES OF SPECIAL CROPS 



73 



sections southwest of Virginia between the parallels of 35° 
and 39° north latitude. In 1900 it was estimated that 




Fig. 24. — Bitter rot caakers in which perithecia were found. After Burrill. 

the loss in four counties of Illinois was $1,500,000. The 
president of the National Apple Shippers Association esti- 



74 DISEASES OF ECONOMIC PLANTS 

mated the damage to the apple crop of the United States 
that year as $10,000,000. There is often a loss of from 
50 to 75 per cent of the crop. 

Two modes of treatment used in conjunction are useful : 
first, to cut off and burn the cankers and to hand pick and 
destroy mummified fruit ; second, to spray the growing fruit 
with a fungicide. The mummified fruit should all be col- 
lected and all cankers, so far as they can be detected by the 
most searching inspection, should be taken out. The trees 
should be sprayed once before the buds open, and frequently 
thereafter until the fruits are almost ripe, with Bordeaux 
mixture, or self-boiled lime-sulphur wash. A non-spotting 
spray should be used for the last application. 

Scab (Venturia inaequalis (Cke.) Wint.). — This is justly 
called the most injurious disease with which the apple 
grower has to contend. It affects both fruit and leaves, 
probably in all localities where apples are grown, and is seri- 
ous in Europe, Australia, and New Zealand, as well as in 
America. 

Upon the fruit, the scab first causes the skin to take on a 
dark olive-green color; later as the outer skin breaks and 
exposes the fungus underneath the color changes to black. 
An apple in this stage is shown in Fig. 25. Still later the 
scab enlarges, and the spores and fungous cells at the center 
of the spot may fall away, leaving a skin of rusty appear- 
ance surrounded by a dark ring where the fungus has not 
yet fallen off. Still further out may be an olive-green or 
silvery ring, showing the still younger stage of the disease. 
Cracking and distortion occur in cases of very badly 
affected fruits. Scabby fruits are much more susceptible 
to bin rot than are clean fruits, p. 94. 



DISEASES OF SPECIAL CROPS 



75 



Upon the leaves and twigs the fungus forms a thick 
velvety coat, varying from dark olive-green to black, in 
spots at first circular in. outline, later irregular and coalesc- 




Fig. 25. — Apple scab. After Craig. 

ing. The irritation and retardation of growth caused by 
the presence of the fungus induces the leaves to curl and 
wrinkle in a characteristic manner. 

The injuries by this disease may be enumerated as 
follows : lessened leaf value, retarded twig and wood 
growth, premature fall of fruit, retardation of full develop- 



76 



DISEASES OF ECONOMIC PLANTS 



ment of fruit, injury to sale of fruit, injury to keeping 
quality of fruit. 

Snow, Spitzenburg, Maiden Blush, Greening, and Twenty 
Ounce are more susceptible than Baldwin, while Golden 

Russet and Hubbards- 
ton are among the 
most resistant vari- 
eties. 

The spray recom- 
mended on page 100 
will to a very large 
extent prevent the 
apple scab. It is es- 
pecially important to 
apply the mixture at 
just the dates indi- 
cated, i.e. just before 
the blossoms open, 
again just after the 
petals fall, followed 
by one or two more sprayings later. 

Blotch (Phyllosticta solitaria Ell. & Ev.). — In some 
sections of this country this disease of bark, leaf, and fruit 
is even more troublesome than any of the preceding, though 
its distinct identity was not recognized until 1897, when 
the first specimens came from Maryland and Texas. 
Since then the disease has been frequently seen in the 
eastern part of the United States though not as a very 
serious pest. Its most destructive center heretofore has 
been in the Ozarks of Arkansas and Missouri, where 75 per 
cent of the crop is commonly rendered unfit for barrel- 




Fig. 26. — Apple blotch (phyllostictose) . 
Scott and Rorer. 



DISEASES OF SPECIAL CROPS 



77 



ing. One county alone is 
estimated to have suffered a 
loss of $950,000. Owing to 
its superficial similarity to the 
scab, it has perhaps been 
confounded with it in some 
instances. The first publica- 
tion concerning the disease 
appeared in 1902, 1 and the first 
detailed description in 1907. 2 

Upon the fruit the blotches 
are from 5-10 mm. in diam- 
eter, dark in color, with an 
advancing margin of very 
peculiar, irregular, jagged, or 
fringed appearance. By co- 
alescence large spots may 
form, and owing to tension, 
cracks appear, enlarging to a 
centimeter in length, or even 
girdling the fruit, and reach- 
ing to the core. In the older 
portions of the blotch, minute 
pycnidia develop. These 
blotches mar the appearance 
of the fruit and injure it as fig. 27.— Apple blotch (phyiiostictose) 
a salable product. ontwigs - 0riginal - 

Upon twigs, spurs, or shoots are produced cankers, 

1 Clinton, G. P., 111. Agr. Exp. Sta. Bui. 69, pp. 190-192. 

2 Scott, W. M., and Quaintance, A. L., U.S. Dept. Agr. Farmers' Bui. 
283, pp. 14-18. 




Ii»il|^ 



78 DISEASES OF ECONOMIC PLANTS 

which, during the first year, consist of small spots 2-10 
mm., tan colored, each bearing several pycnidia. The 
margins of the spots are sharply limited, and are usually 
bordered with a narrow red line. In older cankers the 
diseased bark becomes cracked, furrowed, and much 
roughened. 

On the leaf this fungus causes small, irregular, light 
brown, yellowish, or whitish spots, usually 1-2 mm. in 
diameter, each of which may bear one or several pycnidia. 

The Ben Davis, Missouri Pippin, Limbertwig, North- 
western Greening, Smith Cider, and Maiden Blush are 
highly susceptible, while Winesap, Jonathan, and York 
Imperial are almost immune. 

Ordinarily four applications of Bordeaux mixture suffice 
to control the blotch. The first spraying should be made 
three or four weeks after the petals have fallen; the sec- 
ond about four weeks later ; the third and fourth at inter- 
vals of three weeks thereafter. Careful pruning to re- 
move affected twigs is beneficial. 

Scurf (Phyllosticta prunicola (Opiz) Sacc). — This af- 
fection of the bark of twigs causes it to shrivel. The dis- 
eased part is thickly studded with the very minute pycnidia. 

Affected twigs should be cut out and burned. 

Rust (Gymnosporangium macropus Link). — The rust 
of the apple may usually be readily recognized by its 
characteristic yellowish orange spot on the leaf, or more 
rarely upon the fruit or twig. This spot, yellowish green 
at first, gradually becomes darker, approaching orange. 
Upon close examination, the upper surface of one of 
these discolored spots is seen to contain very numerous 
pustules, at first honey yellow, finally black, smaller 



DISEASES OF SPECIAL CROPS 



79 



than a pinhole, while upon the lower surface of the dis- 
eased spot appear some weeks later the fringe-toothed 
cluster cups. This spot is 
sometimes so abundant 
that its presence upon 
orchards may be recog- 
nized at great distances 
by the characteristic hue 
imparted to the foliage 
mass as a whole. It robs 
the tree of nourishment 
and renders normal fruit- 
age impossible. 

A peculiar relation ex- 
ists, in that the causal 
fungus spends part of its 
life on one plant, the apple, 
and the remainder upon a 
totally different plant, the 
red cedar, the Alternate 
Host of the apple rust. 
The fungus summers upon 
the cultivated apple or the 
wild crab-apple tree, at 
the approach of winter its 
spores are borne by the 
wind from the apple trees 
to an adjacent juniper or 
red cedar tree. There the 
fungus grows and causes the familiar " cedar apple." 

In the spring the cedar apple produces gelatinous, horn 




Fig. 28. 



Apple leaf affected with rust. 
Original. 



80 DISEASES OF ECONOMIC PLANTS 

like projections, each bearing myriads of spores, which, 
when conveyed by the wind to the susceptible apple tree, 
cause the apple rust. Evidence that this relation really 
exists is readily found if one examines an orchard having 
red cedar trees upon its windward boundary. 

It is clear that the more red cedar trees there are in the 
neighborhood of an orchard, especially to windward, the 
more probability there is of damage from the rust. The 
rational treatment, therefore, is to remove these trees in 
so far as possible. 

In rare instances spores may be carried several miles, 
but orchards are reasonably secure if all possibility of in- 
fection from the immediate neighborhood be removed. 
In case the red cedars are too numerous, or if for other 
reasons it is impossible to cut them, spraying the tree as 
recommended for the apple scab will lessen the evil to some 
extent, but its success is not complete or certain. 

Resistant apple varieties are : Duchess, Sweet June, 
Yellow Transparent, Red Astrachan, Ben Davis, Maiden 
Blush, Winesap, Oldenburg, Gano, York Imperial. The 
following are more susceptible : Wealthy, Red June, 
Whitney, Jonathan, Missouri Pippin, Prairie Crab. 

Blight (Bacillus amylovorus (Burr.) De Toni). — De- 
scription and discussion of this disease will be found on 
page 101 under Pear, the blight of which is identical with 
the apple disease. Its character and treatment are the 
same upon both hosts. While the blight is preeminently a 
pear disease, it also affects the apple very seriously, par- 
ticularly the form of " body blight " upon the trunk. 

The Lowell, Isham, Smith Cider, and Yellow Transpar- 
ent are especially susceptible varieties, while the Celestia, 



DISEASES OF SPECIAL CROPS 



81 



Buckingham, Mammoth Black Twig, White Winter Pear- 
main, Winesap, and Ben Davis are resistant, the last al- 
most entirely so. In general the 
crab varieties are more suscep- 
tible than others. 

Black rot, canker (Sphcerop- 
sis Malorum Peck). — In many 
respects this disease closely re- 
sembles the bitter rot, particu- 
larly in that it appears both as 
rot of the fruit and as cankers 
upon the limbs, each of which is 
almost indistinguishable from 
bitter rot upon the similar part. 
In some instances it also appears 
as a twig blight and as a leaf 
spot. 

Upon the fruit the spot, though 
sometimes of a darker hue, is 
often quite indistinguishable from 
that of the bitter rot. As seen 
under the hand lens the coils of 
exuding spores are black, instead 
of pink, as is the case with bitter 

rot. A compound microscope is necessary to bring out 
other distinguishing characters. 

The limb cankers, first studied by Paddock, 1 consist of 
swellings with the bark rough, and black, or in many cases 
expose the black and decayed wood from which the bark 
has disappeared. This cankerous infection sometimes 

1 Paddock, W., N.Y. (Geneva) Agr. Exp. Sta. Bui. 163, December, 1899. 
G 




Fig. 29. — Apple black rot canker 
(sphaeropsose) showing numer- 
ous pycnidia. After Whetzel. 



82 DISEASES OF ECONOMIC PLANTS 

extends for nearly a meter along the branch, and occasion- 
ally girdles it. When occurring upon the trunk or main 
branches, body blight is caused, similar in appearance and 
effects to that mentioned under blight. 

The Tolman Sweet is said to be quite resistant to the 
canker, while Twenty Ounce is very susceptible. Four 
other varieties range in susceptibility as follows : Baldwin, 
Wagener, Greening, King. 

The Sphaeropsis twig blight somewhat resembles the 
fire blight with which it is often associated, but may be 
distinguished from it by the presence of myriads of mi- 
nute pimples distributed thickly over the affected region. 
With a hand lens coils of spores may often be clearly seen 
issuing from these pustules. 

Upon the leaf blighted spots are caused, irregularly cir- 
cular in outline, often marked by concentric rings. The 
body of the spot is brownish and the margin sharply lim- 
ited. Similar spots are caused in several other diseases, 
and definite knowledge of the nature of leaf spots must 
depend upon microscopic diagnosis in each special case. 
Yet it is certain that many of the spots upon apple leaves, 
especially when Sphaeropsis prevails upon fruit and twigs, 
are caused by this fungus. 

The various forms of this disease which have been noted 
in Nebraska, Michigan, Missouri, Ohio, West Virginia, 
Wisconsin, Kentucky, and Vermont, and throughout the 
Allegheny and eastern apple sections, are troublesome 
each year. 

The treatment should be the same as that recommended 
for bitter rot with special care to avoid bark wounds of 
all kinds, as from ladders, workmen's boots, etc. 



DISEASES OF SPECIAL CROPS 



8B 



Pacific coast canker, black-spot canker 1 (Macrophoma 
curvispora Peck) . — The Pacific coast canker is particu- 
larly destructive in the northwestern states west of the 
Cascade Moun- 
tains. It was first 
noted about 1893 
when it developed 
in such destruc- 
tive form as to 
cause the Wash- 
ington State 
Board of Horti- 
culture to call 
upon the Federal 
Government for 
its investiga- 
tion. It has since 
been reported in 
Oregon, Idaho, 
Nebraska, and 
British Columbia. 

The bark or sap- 
wood of twigs and 
larger branches is 
the seat of infec- 
tion, but the dis- 
ease may occur 

also upon the fruit when in storage. T ne loss of an entire 
orchard within a few years has resulted from the black- 
spot canker. Young trees, owing to their tender bark, are 
especially susceptible. 

1 Lawrence, W. H., Wash. Agr. Exp. Sta. Bui. 66, p. 5, 1904. 




Fig. 30. 



Black spot canker (macrophomose). 
Cordley. 



After 



84 



DISEASES OF ECONOMIC PLANTS 



Upon twigs, cankers in the early stage appear as round or 
oval, slightly sunken, dark areas which increase but slowly 
in diameter. As soon, however, as 
the fungus penetrates into the cam- 
bium and sapwood the canker en- 
larges very rapidly, making its most 
rapid development through the cam- 
bium, and advancing more tardily 
through the overlying bark. The. 
resulting spots are nearly circular, 
quite black, and from 5 mm. to 12- 
14 cm. in diameter. When old, the 
bark becomes brittle and a definite 
fissure separates the dead from the 
healthy portions, indicating cessa- 
tion of advance of the fungus. 
Acervuli appear first in the oldest 
parts of the canker, later toward 
the periphery, rupturing the epider- 
mis and exposing the spore masses 
which are at first creamy white, but 
later black. After the spores have 
matured the diseased bark becomes 
separated from the wood and even- 
tually falls away, leaving a scar. 
Branches, or even trees, may be 
killed by girdling cankers. 

Upon stored fruit the disease 

appears first as light brown, cir- 

These later turn very dark or black, 

and tough. Acervuli simi- 







Fig. 31. — Black spot canker, 
After Lawrence. 



cular, rotten spots. 

and become depressed, dry, 



DISEASES OF SPECIAL CROPS 



85 



lar to those upon the bark soon develop in concentric 
circles. 

Lawrence notes the Baldwin, Blue Pearmain, Grav- 
enstein, Newton Pippin, 
Wagener, Wealthy, and 
Yellow Bellflower as espe- 
cially susceptible; the 
Hubbardston, Nonesuch, 
Imperial Pippin, King of 
Tompkins County, Maiden 
Blush, Olympic, Red As- 
trachan, Rhode Island 
Greening, Spitzenburg, 
Striped Astrachan, Twenty- 
ounce Pippin, and Yellow 
Transparent as less suscep- 
tible, while the Northern 
Spy, Waxen, and Ben 
Davis are comparatively 
free from the disease ; but 
these generalizations are 
largely modified by a great 
variation in resistance 
among individual trees. 

When the cankers are 
few, on small trees, excision 
may be practiced to advan- 
tage; when, however, there are hundreds of cankers upon 
each tree, this treatment is manifestly impracticable. 
Spraying with strong Bordeaux mixture, 12-8-50, in the 
fall after the crop is gathered is valuable to prevent the 




Fig. 32. — Black spot on fruit. 
After Lawrence. 



86 DISEASES OF ECONOMIC PLANTS 

formation of new cankers, and has established practical 
control of the disease. 

Illinois canker (Nummularia discreta (Schw.) Tul.). — 
Attention in America was first called to this as an active 
parasitic disease in 1902 by Hasselbring, 1 who attributed 
to it more serious results than from any other canker 
disease of Illinois. It has been reported from West Vir- 
ginia, Missouri, Arkansas, and Nebraska. 

The cankers are at first inconspicuous, unhealthy, dirty 
brown, usually depressed spots in the bark, sometimes 15 
cm. in diameter, which enlarge rapidly, particularly length- 
wise upon the limb, a crack often marking the boundary 
between dead and sound bark. The interior of the bark 
of such spots is mottled with dead regions. 

In autumn the sporiferous bodies appear near the borders 
of the diseased spots, first pushing through cracks in the 
bark, and exposing pale grayish ochre-colored fungous 
growths 3-6 mm. in diameter, which, when mature, are 
slightly saucer- or dish-shaped, and dark in color. These 
bodies are attached to the dead wood, and remain there 
even after the bark has fallen away, thus constituting a 
diagnostic character of absolute reliability, separating this 
from all other cankers. Discoloration of the heartwood 
often occurs at a distance of a meter or more from the 
apparent seat of disease. 

When the cankers become large, injury to the distal 
parts through interruption of the water supply results. 
The leaves show symptoms of disease, and the fruit fails 
to grow to full size. With complete girdling the limb dies. 

Since all infection seems to occur through wounds, pre- 

i Hasselbring, H., III. Agr. Exp. Sta. Bui. 70, April, 1902. 



DISEASES OF SPECIAL CROPS 87 

vention must look largely toward the avoidance of wounds 
by tools, machinery, harnesses, pickers' ladders, boots, etc. 
It is also an excellent sanitary measure to cut out and burn 
all infective material, and even excision of diseased tissue 
in a limb may be practiced with profit in incipient cases. 

European canker (Nectria ditissima Tul. and Nectria 
cinnabarina (Tode) Fr.). — The European canker was not 
recorded upon the apple in America prior to 1899, 1 when 
Paddock mentioned its presence in Nova Scotia and New 
York. Later it was noted in New Hampshire. It con- 
stitutes a serious disease in Europe and may spread so as 
to be injurious here. The canker enlarges year after year, 
but more slowly than the Sphaeropsis canker, and displays 
when fruiting numerous minute, deep red perithecia which 
serve to distinguish it from other cankers. 

Bark canker (Myxosporium corticolum Edg.). — This 
canker in general aspect closely resembles the cankers 
previously mentioned, except that the injury does not 
penetrate the cambium zone. It is of little economic 
importance. 

Leaf spot (see also black rot) . — Aside from the leaf 
diseases of apple already mentioned there are numerous 
other leaf spots due to various, partly to unknown, causes. 
These spots partake of the same general character. That 
is, they are brown to tan colored, at first circular, later 
irregularly circular, definitely bordered, and usually concen- 
trically marked. If abundant, or if they enlarge rapidly 
upon the leaves, they cause their premature fall, and 
largely defoliate the tree. Such spots prevail to greater 
or less extent in all apple orchards. Numerous species of 

1 Paddock, W., Sci. n. s. 12, 297. 



88 



DISEASES OF ECONOMIC PLANTS 



fungi have been isolated 
from these spots, 1 some 
of them may sustain a 
causal relation to the 
disease. 

Whatever the actual 
causal fungus may be, 
these spots are all, or 
nearly all, of fungous ori- 
gin and are amenable to 
preventive spraying with 
Bordeaux mixture. The 
first of three or four 
applications should be 
given with the opening 
of the leaf buds. 

Illosporiose, leaf spot 
(Illosporium malifolio- 
rum Shel.). — This is 
said by Sheldon 2 to be 
the cause of much of the 
defoliation of apple or- 
chards in West Virginia 
and adjacent states. 
The spots are circular, 
5-15 mm. in diameter, brown or mottled and gray, con- 
centrically marked. 
For treatment see page 100. 

1 Notably by Hartly, Minnesota, and by Lewis, I. M., New Hampshire 
Agr. Exp. Sta. Rpt. 19-20, November, 1908. 

2 Sheldon, J. L., Torreya, 8, 141, June, 1908. 




Fig. 33. — Apple leaf spot in late stage of 
development, showing concentric rings. 
Original. 



DISEASES OF SPECIAL CROPS 



89 



Hypochnose 1 (Hy- 
pochnus ochroleuca, 
Noack). — Hypoch- 
nose is principally a 
leaf affection causing 
blight and loss of the 
leaves, and thereby 
weakening the vital- 
ity of the tree. 

Superficially this 
disease resembles the 
blight, with which it 
might be confounded 
by the casual ob- 
server. It may be 
readily distinguished, 
however, by two char- 
acters: first, the 
manner in which the 
leaves droop and mat 
together, which is 
quite different from 
the habit of the blight, 
the leaves of which 
neither droop nor 
mat; second, by the 
presence of small scle- 

rotia, white when young, cinnamon-brown when mature, 
upon the twigs adjacent to the affected leaves. These 
sclerotia usually measure about 2-3 mm. in diameter. To- 

1 Stevens, F, L., and Hall, J. G., Ann. Mycol. VII, 49, 1909. 























S3 


*§;:■£- ■> 


V / *d 






ft 


>■'■• 


■ V 







Fig. 34. — Hypochnose, showing matting of leaves. 
Original. 



90 



DISEASES OF ECONOMIC PLANTS 




Fig. 35. — Hypochnose, showing sclerotia 
on twig at left and rhizomorphic strands 
on twig at right. Original, 



gether with the sclerotia 
and extending along the 
twig longitudinally are 
also found silvery, glis- 
tening, thread-like, fun- 
gous growths. 

This fungus hibernates 
in the sclerotia on or near 
the terminal bud and 
thence invades the new 
twigs as they develop, 
reaching out upon each 
leaf, spreading over its 
under surface in almost 
invisible thinness, and 
causing it to droop, die, 
and eventually to fall 
away. Thus in early au- 
tumn such trees are nearly 
or quite defoliated. The 
fruit may be also invaded 
by the fungus. This an- 
nual premature loss of leaf 
is a serious injury to the 
tree, hindering its proper 
growth and preventing 
proper fruitage. 

Hypochnose, first de- 
scribed from Brazil, is 
known from Maine to 
Florida in the United 



DISEASES OF SPECIAL CEOPS 91 

States. It seems to be especially destructive in regions 
of excessive humidity, particularly in the deep mountain 
valleys of the Appalachians, where whole orchards are 
sometimes seriously affected. 

Owing to the entirely superficial nature of the fungus 
which causes the disease, and its habit of hibernating upon 
the twigs, the trees should be sprayed with a strong cleans- 
ing mixture, Bordeaux or bluestone, before the buds open, 
and again just before the blossoms open. 

Fruit rot (Hypochnus sp.). — Eustace 1 first described this 
rot of the fruit upon Baldwins and Rhode Island Green- 
ings. In that it follows scab it is similar to pink rot, to 
which in appearance it also bears superficial resemblance. 
A distinguishing feature of this disease is that there is 
normally no large surface growth of fungus in the center of 
the diseased spot. In this disease the rot often extends to 
the core, while in the other similar diseases the spot is 
shallow. 

The treatment is the same as for pink rot. 

Pink rot (Cephalothecium roseum Cda.). — This rot, 
known in many states, is stated by Eustace 2 to be par- 
ticularly prevalent in western New York. It follows apple 
scab and may be recognized by the white, mildew-like 
growth which appears in conjunction with the scab and 
soon after entirely overgrows it. 

While the decay is really caused by the Cephalothecium, 
the rupture made in the skin by the scab fungus is the' usual 
place of entrance. The -decayed spot is shallow and slow 

i Eustace, H. J., N.Y. (Geneva) Agr. Exp. Sta. Bui. 235, July, 1903. 
2 Eustace, H. J., N.Y. (Geneva) Agr. Exp. Sta. Bui. 227, December, 
1902. 



92 



DISEASES OF ECONOMIC PLANTS 



growing as compared with other rots. It is accompanied 
by a bitter taste which is so pronounced as to injure cider 
made from affected apples. The chief destruction follows 
the harvest, though the disease is sometimes found in 
fruit still upon the tree. 

The Rhode Island Greening, Fall Pippin, Fameuse, 




Fig. 36. — Pink rot (cephalotheciose) following scab. After Eustace. 



Maiden Blush, Tompkins King, and Twenty Ounce are 
especially susceptible. 

Chief attention should be directed to the prevention of 
the scab. In storage a dry house, well ventilated, kept 
at 45° F. or below gives best rot resistance. 

Brown rot (Sclerotinia fructigena (Pers.) Schroet.). — 
One of the most serious apple rots in Europe, this disease 
is fortunately as yet less destructive in America, though 
it is occasionally met with as one of the minor causes of 



DISEASES OF SPECIAL CROPS 



93 






apple losses and has been noted in several states, notably 
Missouri, Nebraska, West Virginia, and North Carolina, 
in abundance enough to call for printed mention. 

Brown rot produces complete decay of the affected apples, 
which turn brown, become soft and wrinkled, and soon 
show pustules of bushy mycelium breaking through rifts 
and fissures in the skin over the diseased tissue. The 
diseased fruits may 
mummify upon the 
tree or more fre- 
quently fall to the 
ground and there 
shrivel to dry, hard, 
wrinkled masses, in 
which the rot fungus 
winters. 

Powdery mildew, 
Sphser othecose 
(Sphcerotheca mail 
(Duby) Burr.).— 
The general appear- 
ance of this mildew is much like that described for the 
grape ; that is, the surfaces of the leaves are more or less 
covered with a white or grayish fungous growth, in the 
later stages of which are found numerous very small black 
fruiting bodies approximately 0.25 mm. in diameter. This 
fungus, while of comparatively little significance to old 
apple trees, causes much injury to nursery stock, often be- 
coming so serious as to prevent successful budding. Mil- 
dew has been reported as serious in California and other 
western states, — in Kentucky, Iowa, Washington, and 




Fig. 37. — Brown rot (sclerotiniose) produced by 
inoculation. Note the fungus forms the letters 
A. M. C. Original. 



94 DISEASES OF ECONOMIC PLANTS 

West Virginia. The use of ammoniacal copper carbonate 
as the leaves unfold, and continued at intervals of two 
weeks until budding time, will usually prevent damage from 
the disease. Sulphur or sulphide sprays have given best 
results in dry climates. 

Podosphaerose (Podosphcera leucotrichia (Ell. & Ev.) 
Salm.). — This mildew is similar to Sphserothecose. 

Crown gall. — See peach. 

Soft rot, bin rot, blue mold (Penicillium glaucum Link). 
— Perhaps the most common apple rot is found upon 
stored apples late in the year. The light tan-colored 
rotten area is soft and watery. The decay results in the 
complete loss of the affected fruit, and, by contagion, in 
loss to the fruit mass. 

Upon cracks in the rotted surface, and eventually over 
the whole rotten part, appear tufts of very short delicate 
fungous threads, at first white, soon bluish green, very like 
the common blue mold so familiar to the housewife upon 
canned fruit, the seal of which has permitted air to enter. 
This blue substance upon the rotten apple consists of 
myriads of the spores of the causal fungus. This fungus 
is comparatively unaggressive and cannot force its way 
into perfectly healthy tissue ; a bruise or rupture of the 
skin is necessary to its invasion. The best preventive 
is care to avoid bruising. 

Sooty blotch (Phyllachora pomigena (Schw.) Sacc). — 
Irregular, sooty, black blotches, especially conspicuous 
on the lighter colored varieties, are frequently seen upon 
unsprayed fruit. 

The individual blotches measure from 0.5-2 cm. across 
and are often so abundant that they coalesce, giving the 






DISEASES OF SPECIAL CROPS 



95 






fruit a dirty appearance. The fungus attacks the fruit 
late in the season, and is strictly superficial. It may be 
easily rubbed off with a cloth. The loss in ready salability, 
due to the unsightliness of the fruit, is reason enough for 
protective spray- 
ings. 

The Bordeaux 
mixture applied at 
intervals of about 
two weeks from 
the middle of June 
until the middle 
of August is effec- 
tive. 

Flyspeck (Lep- 
tothyrium pomi 
(Mont. & Fr.) 
Sacc.) . — Growing 
upon the surface 
of the fruit and 
forming numerous clustered black specks closely resembling 
fly specks, this disease causes disfigurement of the apple. 
Though the disease is of very wide distribution, the loss 
occasioned by it is not serious and is almost entirely pre- 
vented by the sprayings employed against other diseases. 

Coniothyriose (Coniothyriwn Fuckelii, Sacc). — A rot 
upon fruit very similar to bitter rot, and a twig blight 
very similar to Sphseropsose is caused also by Coniothy- 
rium. This disease is of less importance than the others 
mentioned, and the remedies already given suffice. 

Volutellose (Volutella frudi S. & EL). — In general 




Fig. 38. — Apple flyspeck. Original. 



9b DISEASES OF ECONOMIC PLANTS 

appearance Volutellose is not to be distinguished from 
SphaBropsose, though the texture of the rotted tissue is 
much firmer and dryer. Under the hand lens the sporif- 
erous pustules are seen to be clothed with numerous hairs, 
which character sufficiently marks it as a separate disease. 
As yet it has been reported only from North Carolina. 1 

New Hampshire fruit spot (Cylindrosporium pomi 
Brooks) . — This disease, which has been noted in Delaware, 
New York, Pennsylvania, Michigan, Maine, Massachusetts, 
New Hampshire, Toronto, and Montreal, appears in late 
summer as very small, deep red, slow-growing spots, usually 
at the lenticels. A little later these spots turn brown and 
then resemble closely the young spot of black rot or ripe 
rot in appearance though not in texture. At or after 
harvest the spots are somewhat depressed, through failure 
of the sick tissue to keep pace in growth with the surround- 
ing tissue. This disease has been demonstrated by Brooks 2 
to be of fungous origin and to be amenable to treatment by 
the Bordeaux mixture applied late in June or early in July. 

Black mold (Alternaria sp.). — -The blossom end of the 
fruit is affected by the rot. The spot is dark purplish 
to brown and slightly sunken, enlarges very slowly, and 
may not be noticeable until the fruit is in storage. 
Often no disease is noted until the apple is cut through, 
when the core is found blackened and discolored, and 
the seeds covered with the dark mycelium. In more 
serious cases the effect extends into the surrounding pulp. 
This black mold was first described by Longyear. 3 

i Stevens, F. L., and Hall, J. G., N.C. Agr. Exp. Sta. Bui. 196, p. 41, 

2 Brooks, Charles, N.H. Agr. Exp. Sta. Rpt. 19, 1908. 

3 Longyear, B. O., Colo. Agr. Exp. Sta. Bui. 105, 1905, 



DISEASES OF SPECIAL CROPS 



97 




Fig. 39. — Clitocybe upon apple. After Wilcox. 

The Lawver, Loy, Mann, Dominie, Jonathan, Ben Davis, 
and Winesap are especially susceptible. 

The methods of treatment recommended are clean cul- 
ture, a cleansing spray, and one or two applications of a 
preventive spray. 

Texas root rot. — This is destructive to apples in the re- 
gions where it prevails. See cotton. 



98 DISEASES OF ECONOMIC PLANTS 

Wound infections and wood rot. — See general discussion 
of the subject, p. 410. 

Wood rot (Schizophyllum commune Ft.). — Decay of the 
roots and lower trunk occur here much as in cherry. 




Fig. 40. — Unsprayed apple trees. After Scott and Rorer. 

The causal fungus seems to enter through wounds in the 
bark or roots. Later the characteristic sporophores are 
produced. See page 120. 

Clitocybose, root rot (Clitocybe parasitica Wilcox). — 
This root rot, very similar to that caused by Armillaria 
mellea, p. 173, was described by Wilcox in Oklahoma 
in 1901 1 as characterized chiefly by a copious exudation 
of gum from the crown of the diseased trees. The leaves 

1 Wilcox, E. Mead, Okla. Agr. Exp. Sta. Bui. 49. 



DISEASES OF SPECIAL CROPS 



99 



turn yellow or wilt and black mycelial strands are found 
in abundance attached to the roots. Later, groups of 
sporophores are found about the base of the tree. These 




Fig. 41. — Sprayed apple trees from the same orchard. After Scott and Rorer. 

in general resemble the sporophores of Armillaria. See 
page 425. 

The isolation of diseased trees by trenching may pre- 
vent the infection of other trees. Orchards should not be 
located in soil containing old oak stumps. All infected 
material should be burned. 



Combination Treatment for Apple Diseases 

The following treatment is designed to meet all of the 
fungous enemies of the apple. In event certain diseases 



100 DISEASES OF ECONOMIC PLANTS 

are absent, this treatment may be modified in the light of 
what is said on preceding pages. 

1. Employ methods 6, p. 20, and 9, p. 21. 

2. Apply a cleansing spray No. 3, p. 18. 

3. Use protective sprays No. 4, p. 18 : 1st, before 
blossoms open; 2d, after petals fall; 3d, three or four 
weeks later; 4th, about five weeks after the third; 5th, 
about three weeks later; 6th, about three weeks later. 

Bordeaux Injury to Apples 

Ever since the first trials of Bordeaux mixture upon the 
apple some injury has been noted upon both leaves and 
fruit, due to this mixture itself, the amount of injury 
differing with different varieties, and with the weather 
conditions. 

The injury may first appear a few days after spraying 
or may be delayed for weeks, showing first on the fruit as 
small, round, black specks, which later become rough and 
russeted, and in severe cases distorted and badly scarred. 
Such fruit does not keep well, becoming mealy or soft. 
Upon the leaves brown dead spots are caused, often 
followed by yellowing and fall of leaf. Blossoms are 
killed, and the lives of visiting bees may be endangered. 
These effects are worse in wet weather, also when large 
amounts of copper sulphate are used than with smaller 
amounts. 

This injury is far less than the fungous injury avoided 
by use of the mixture, but should be reduced to , a mini- 
mum by spraying only when needed, giving less mixture 
to those varieties which possess fungous resistance, and 
to those varieties which prove most susceptible to Bor- 









DISEASES OF SPECIAL CHOPS 101 

deaux injury. The use of too much Bordeaux, so that 
it drips from the leaves, increases the Bordeaux injury, 
as does also the presence of too much copper in the 
mixture. 

PEAR 

Blight, fire blight (Bacillus amylovorus (Burr.) De Toni). 
— The name " fire blight " is well chosen, since the affected 
tree, with its shriveled branches and shrunken, blackened 
twigs, gives the impression of fire injury. 

During winter the disease may best be recognized from 
the fact that the leaves of the diseased twigs do not fall as 
do those of healthy twigs. In the early spring, when the 
disease is most aggressive, the blighted twigs may be known 
at a glance by their dead black leaves, while on closer 
examination the bark and wood a*e seen to be black and 
dead. This blight is the worst disease of the pear and is 
also bad on the apple, quince, and hawthorn, and to some 
extent affects plum, apricot, and mountain ash. 

It has been known for more than a hundred years, and 
in many cases even whole orchards have succumbed to 
its attack. One pear grower near Washington, D.C., 
estimated his loss from this one disease in one year at 
$10,000. The disease is widely known throughout the 
United States, but is as yet confined to North America. 

So diverse and numerous were the early theories as to 
the nature and cause of blight and so fruitless were the 
discussions in earlier years that the western New York Hor- 
ticultural Society passed resolutions to prohibit further 
reference to the subject until entirely new facts were forth- 
coming. Among the numerous theories might be men- 



102 



DISEASES OF ECONOMIC PLANTS 



tioned, those depending upon electrical or atmospherical 
influences, freezing of the bark, too long culture of par- 




Fig. 42. — Pear blight ; healthy and diseased twigs. Original. 



ticular varieties, freezing of the roots, too high culture, 
insects, fungi, and absence of needed food. One of the 



DISEASES OF SPECIAL CROPS 103 

most prominent of these was Downing's " frozen sap 
theory," according to which the disease is due to the freez- 
ing and thawing of the sap, resulting in loss of vitality and 
development of poisons in the tissues. It is unnecessary 
to discuss any of these theories further than to say that 
none of them explain the facts. 

In 1878, Professor Burrill 1 discovered bacteria in the 
diseased twigs, and by transferring to healthy twigs some 
of the exudate from diseased tissue bearing these bac- 
teria was able to cause the disease. Professor Arthur 
later grew the bacteria in pure cultures and with these 
cultures produced the disease. It was thus proved be- 
yond question that it is these bacteria that cause the 
blight. 

It has been demonstrated that the germs cannot gain 
access through healthy mature bark, but will readily pene- 
trate into any wounded place, or into floral parts. 

This blight bacillus deposited upon the flower or upon 
tender shoots gains entrance and rapidly grows downward 
through the cambium, causing the foliage upon the affected 
twig to die. The disease rarely progresses more than 5-8 
cm. in one day, though even 0.3 meter is occasionally 
reached. Ordinarily, sick twigs dry out, progress of the 
disease soon stops, and the germs in the twig die. Waite 2 
found that in some limbs, probably one of several hundred, 
the disease remains active. Two forms of the disease are 
thus distinguished: one very dangerous, the other no 
longer offensive. It is these limbs still in condition of 
" active blight " that carry the pest over winter. 

1 Burrill, T. J., Trans. 111. Hort. Soc. for 1878, p. 80. 
, 2 Waite, M. B., U.S. Dept. Agr. Yearbook, 1895, p. 295. 



104 



DISEASES OF ECONOMIC PLANTS 




Fig. 43. — The blight showing exudate from 
bark, much enlarged. This teems with the 
causal bacteria. After Whetzel. 



With the flow of sap in the spring these infested limbs 
become centers of reproduction. From these a milky fluid 
teeming with the bacteria exudes. This attracts insects 
which then carry the infection to other twigs and to flowers. 
Two additional forms of this disease, according to the part 

affected, are recognized: 
(1) flower blight, (2) 
body blight and canker. 
Neither of these differs 
essentially from the twig 
blight, though the body 
blight or canker is es- 
pecially worthy of men- 
tion on account of its 
peculiar destructiveness. 
This form occurs where 
the disease is led by a spur, shoot, or sucker into the cam- 
bium under the bark of the body or main limbs of the tree, 
or where primary infection occurs through a wound so as 
to lead to disease in such parts. The result of such in- 
fection is a diseased area more or less circular, which may 
even girdle the tree or branch, and which in any event 
causes serious injury. 

The susceptibility of the tree is largely influenced by 
external conditions. In general, anything which leads to 
rapid growth, resulting in tender shoots, favors the devel- 
opment of the disease. There is also much difference 
in resistance offered by different varieties. The Anjou, 
Kieffer, Angouleme, and Seckel possess more resistance 
than the Bartlett, Clapp, or Flemish Beauty. 

Based on the facts as stated above, the following direc- 









DISEASES OF SPECIAL CROPS 105 

tions for avoiding the blight were deduced, and tested by 
Waite. 1 They have proved their worth in many states. 2 

1. Pruning in winter when the tree is dormant pro- 
motes growth and favors blight. Withholding the pruning 
knife, which may not otherwise be best for the tree, will 
reduce this tendency. 

2. Overstimulation with fertilizers, especially those 
rich in nitrogen, is to be avoided. 

3. A well-cultivated tree is more inclined to blight 
than one growing on sod or untilled land. 

4. In irrigated orchards a reduction of the water supply 
to the minimum has been found effective. 

5. The only really satisfactory method of controlling 
pear blight (that is, exterminating the microbe that 
causes it) is by cutting out and burning every particle of 
blight when the trees are dormant. Not a single case of 
blight should be allowed to survive the winter, either in the 
orchard or within half a mile of it. Every pomaceous 
tree, including the apple, pear, quince, Siberian crab apple, 
wild crab apple, the mountain ash, service berry, and all 
the species of Crataegus, or hawthorns, should be examined 
for this purpose, the blight being the same in all. The 
orchardist should not stop short of absolute extermination 
in every case, for a few trees or branches overlooked may 
go a long way toward undoing all his work. Cutting out 
the blight may be done at any time in the winter or spring 
up to the period when growth begins. The best time, how- 

1 Taken in modified form from M. B. Waite, U.S. Dept. Agr. Yearbook, 
1895. 

2 Whetzel, H. H., 'and Stewart, V. B„ N.Y. (Cornell) Agr. Exp. Sta. 
Bui. 272. 



106 DISEASES OF ECONOMIC PLANTS 

ever, is undoubtedly in the fall, when the foliage is still on 
the trees and the contrast between that on the blighted 
and that on the healthy limbs is strong. It is further 
necessary to make a weekly inspection of every tree through- 
out the growing season, beginning when the blossoms fall, 
and to cut out blight whenever it is found. 

In each case it is necessary to cut well below any external 
evidences of the disease. To avoid spreading the infec- 
tion, in case the pruning tools should accidentally cut into 
the diseased tissue, the cutting blade should each time be 
disinfected by wiping it with a cloth saturated with a 
strong solution of corrosive sublimate (1 part to 1000). 
When the wound made by this excision is at all large, it 
should be disinfected with the corrosive sublimate solution. 
Particular care should be taken to remove and burn all dis- 
eased spurs and watersprouts. 

Unless continued careful inspection is given, but little 
benefit will follow. 

Rust (Gymnosporangium globosum Farl.). — The rust of 
pear is very similar in nature to the rust on the apple, though 
less often injurious. It consists of two stages, a summer 
stage and a winter stage. The summer stage produces the 
rust on the leaves of the pear, while the winter stage forms 
the familiar cedar apple upon the cedar tree. 

The remedy, as in the case of the apple, consists in re- 
moving all red cedar trees from the neighborhood of the 
pear orchard; thus eliminating the source of infection. 
When this is impossible, the trees should be sprayed with 
the Bordeaux mixture immediately after the early rains 
which cause the gelatinous horns on the cedar apple, and 
thus furnish the supply of spores for the spring infection. 



DISEASES OF SPECIAL CROPS 



107 



This disease of pears is particularly abundant upon sev- 
eral varieties of the Japanese strain. 

Bitter rot, ripe rot (Glomerella rufomaculans (Berk.) 
Spaul. & von Schrenk). — This disease is of much less 
frequent occurrence upon the pear than upon the apple. 
For description and treatment, see pp. 64 and 74. 







Fig. 44. — Scab on California pears bought in Raleigh. Original. 



Powdery mildews, sphaerothocose and podosphaerose. 
— See apple. 

Scab (Venturia pyrina Aderh.). — This scab much 
resembles that of the apple and consists of a surface blotch 
or scab, often accompanied by a peculiar cracked appearance 
of the skin. This symptom, however, is a secondary effect 
which is not necessarily present. Upon the twigs rough 
cankers are formed. 

Smith 1 of California recommends plowing under or 
clearing away dead leaves and using a dormant spray fol- 
lowed by two applications of Bordeaux mixture while 

1 Smith, R. E., Cal. Agr. Exp. Sta. Bui. 163, p. 17, 1905. 



108 



DISEASES OF ECONOMIC PLANTS 



*» * *i00^ ^ 



the buds are unfolding, first using an 8-10-50 mixture; 

second a 5-7-50 mixture. 

Leaf spot (Septoria piricola Desm.). — The leaf spot, 
while rarely completely destruc- 
tive to foliage or crop, does 
interfere with the general pro- 
ductiveness and health of the 
tree by diminishing its green 
surface and sometimes by caus- 
ing defoliation. It is known 
over a wide range. 

The leaf spot may be. distin- 
guished from the scab and the 
blight by the fact that the dis- 

r eased area is rather sharply 

defined and characteristically 
angular in outline. The center 
of the spot, usually ashen in 
color, is surrounded by a narrow 
brown zone, and this in turn by 
one of purplish hue. The ashen 
center bears several very mi- 
nute dark-colored pycnidia. 
The treatment recommended 
for pear scab is effective in pre- 
venting this disease. 
Leaf blight (Fabrcea maculata (Lev.) Atk.). — This leaf 
blight is almost as widely distributed as is the pear itself, 
though less abundant in the South and West than in 
the North and East. Its spot does not exhibit the striking 
zonal arrangement described for the leaf spot (septoriose), 



Fig. 45. — Pear leaf spot (septo- 
riose) . Original. 



DISEASES OF SPECIAL CROPS 109 

than which it is a much more serious pest, and the whole 
leaf more often takes on a diseased appearance, eventually 
turning yellow or brown and falling. This disease is also 
prevalent upon the fruit, where it causes a red spot, which 
soon becomes darker, and may later be accompanied by 
cracking similar to that of the pear scab. 

The treatment already recommended for the pear scab 
will suffice for the pear leaf blight. 

Black rot canker (Sphceropsis malorum Peck). — In 
appearance and treatment this disease is similar to the 
black rot of the apple. 

Anthracnose (Colletotrichum sp.). — Diseased pear trees in 
New Jersey were noted in 1892 by Stevens, nearly every 
fruit upon the tree being destroyed. While very serious, 
it is, fortunately, not of frequent occurrence. In nature, 
cause, and appearance it resembles closely the bitter rot of 
the apple, and the treatment may be the same as for that 
disease. 

Hypochnose. See apple. 

Brown rot. See apple. 

Thelephorose (Thelephora pedicellata Schw.). — This 
appears in the form of spots 5 mm. to 8 cm. or larger 
on the trunk of the tree near a dormant bud, on branches 
at the bases of fruit spurs, or at the bases of other branches. 
The spots are nearly circular, surrounded by a whitish, 
uneven edge. Older, larger spots are depressed and the 
bark, cambium, and wood beneath are dark and dead. 

Galloway 1 recommended excision of the diseased wood, 
followed by washing with sulphate of iron (copperas) 
and covering with grafting wax or some similar substance. 

1 Galloway, B. T., Jour. Mycol., 6, 113, 1891. 



110 



DISEASES OF ECONOMIC PLANTS 



Texas root rot. See cotton. 

Black mold (Alternaria sp.). — In addition to the ravages 
of this disease as upon the apple, the leaves and shoots 
are also attacked and the fruit injury is not limited to 




Fig. 46. — Young quinces showing rust. After Bailey. 

the blossom end. The disease has been noted chiefly upon 
the Kieffer. 

For treatment, see apple. 

QUINCE 

Rust (Gymno sporangium clavipes C. & P.)- — The 
quince rust, spring stage, agrees with the apple rust in 
general characters. The causal fungus grows upon the 
fruit in the summer and produces there myriads of spores 
which, on the approach of fall, are carried by the winds to 



PIS EASES OF SPECIAL CROPS 



111 



adjacent cedar trees, and there produce swellings upon 
the branches and twigs during the fall and winter. In the 
spring, these give origin to long gelati- 
nous horns, which consist of masses of 
spores embedded in a matrix of jelly. 
These spores upon drying are conveyed 
to the quince tree by the winds, and 
there produce again the quince rust. 
The cedar is a necessary resting place 
for this fungus dur- 
ing the winter. 

The remedy there- 
fore is, if possible, 
to remove the cedar 
trees from the neigh- 
borhood of quince 
trees. This will al- 
most entirely pre- 
vent the rust, 
although in rare in- 
stances a few spores 
may be carried a 
considerable dis- 
tance. Reasonable 
protection is secured 
if all of the cedar 

trees in the immediate vicinity of the orchard be removed. 
In case the cedar is too abundant to permit of its complete 
removal, resort must be had to spraying the leaves and 
fruit of the quince trees with the Bordeaux mixture at the 
time when the rust spores are expected to arrive; that is, 




Fig. 47. — Quince knot 
caused by the rust fun- 
gus. After Bailey. 



112 DISEASES OF ECONOMIC PLANTS 

at the time when the gelatinous horns are present on the 
cedar apple. 

Blight {Bacillus amylowrus (Burr.) De Toni). — This 
disease has been thoroughly discussed in connection 
with the pear and apple. It is only necessary here to 
indicate that it is the most serious known disease of the 
quince. The treatment is the same as that recommended 
for this disease on other pomaceous fruits. 

Leaf blight, fruit spot (Fabrcea maculata (Lev.) Atk.). — 
Both the fruit and foliage are affected by this blight, 
the foliage spotting and falling prematurely so that the 
vitality and vigor of the tree is much reduced. Upon the 
fruit it causes black blotches, first seen as small brown spots 
which soon increase in size and turn darker in color. While 
this spot does not materially injure the fruit for use, it does 
retard its full development and because of impaired beauty 
decreases its selling price. 

The means of prevention consists in protecting parts 
which have not yet been attacked by a thorough applica- 
tion of Bordeaux mixture. Repeated trials have shown 
that this treatment is thoroughly effective, increasing the 
value of the quince crop very materially; the increase 
being both in the size and the quality of the fruit. The first 
application should be made soon after the blossoms fall, 
and should be followed at intervals of two or three weeks 
with two more treatments. 

Black rot (Sphceropsis malorum Peck) . — This rot, often 
amounting to a loss of 10 per cent, and being widely 
distributed, is due to the same fungus which causes the 
black rot of the apple, and the treatments recommended 
for the apple will prove efficient for the quince disease. It 



DISEASES OF SPECIAL CROPS 



113 



has not yet been proved that this fungus causes cankers 
on the quince trees such as have been described for the 





Fig. 48. — Black spot of the quince, natural size. After Bailey. 



apple. The grower should, however, watch carefully for 
the presence of canker, as the relation between the canker 
and the rot in apple indicates that the canker may possibly 
be found on the quince also. 
i 




Fig. 49. — Quince leaf blight ; twig at right sprayed ; twig at left not sprayed. After Bailey. 



DBUPACEOUS FRUITS 115 

Ripe rot {Glomerella rufomaculans (Berk.) Spaul. & von 
Schrenk). — This disease is caused by a fungus identical 
with that causing the ripe rot of the apple. The treatments 
already recommended for other diseases will also prove 
efficient here. 

European canker (Nectria cinnabarina (Tode) Fr.), 
(Nectria ditissima Tul.). — This canker is readily distin- 
guished from the ordinary cankers produced by Sphseropsis 
or Glomerella by its brilliant red or cinnamon-colored 
pustules scattered abundantly over the affected areas. 
While cankers due to each of these fungi have been 
collected upon quince in America, no case of serious injury 
is known. 

Pale rot (Phoma Cydonioe Sacc. & Schulz.). — This 
disease is second only to the black rot in prevalence and 
destructiveness. The rot begins as a pale soft spot, from 
which the skin can easily be removed. This spot soon 
wrinkles, the skin ruptures, and through the ruptured 
places short tufts of fungous threads develop. These small 
spots are at first colorless, but they soon turn to a pale blue. 

The treatment is the same as for sphseropsose. 

Hypochnose. See apple. 



DRUPACEOUS FRUITS 
ALMOND 



Yellows. See peach. 
Blight (Coryneose). See peach. 
Crown gall. See peach. 
Cercosporose. See peach. 



116 



DISEASES OF ECONOMIC PLANTS 



APRICOT 

Yellows. See peach. 

Phyllostictose. See peach. 

Brown rot. See peach. 

Blight (Bacillus amylovorus (Burr.) De Toni). — The 





-Jg? 


7* , -*? 














-■< 


^§8*3® 


ll^^Plf 










SEpt&vnFI 










%f 






;;^y^. 












"*- .;. "_-5\" 












|iA , *;. 


/j'yki^m 


«^§^ 


;.vv^. 


ySSkkt: 


f»^S 


Jtp^^^fe^ 




i ^JH| -v " 1 S' 












'■•'■*■: *-r.. 




Y~ 




.',."'"■ T ' 



Fig. 50. — Unsprayed cherry tree defoliated by leaf spot. After Scott. 

usual blight of the apple and pear has been reported upon 
the apricot by Paddock. 

CHERRY 

Leaf spot (Cylindrosporium Padi Karst). — For de- 
scription, see plum. The disease is very widespread 
throughout the United States, and it is often very de- 
structive. The loss in Ohio in one year was estimated at 



DRUPACEOUS FRUITS 



117 



$25,000. This disease is identical with that of the plum, 
but since the spraying mixture adheres to the fruit, it cannot 
be applied on to the plum without injury to the market 
value of the product. Spraying as for plum leaf spot with 




Fig. 51. — Cherry tree from same orchard sprayed with self-boiled lime-sulphur to 
control leaf spot. After Scott. 

such modifications as are needed to avoid spotting the fruit 
is the only recourse. 

Recent experiments by Scott l showed that the self-boiled 
lime-sulphur wash (10-10-50), the factory-boiled lime- 
sulphur wash (1-40), and the Bordeaux mixture (2-4-50) 
were equally effective in controlling the cherry leaf spot. 

1 Scott, W. M., U.S. Dept. Agr. Bur. Plant Indus. Circ. 27, April 21, 
1909. 



118 



DISEASES OF ECONOMIC PLANTS 



The results are shown in the accompanying figures. The 
trees, located in Illinois, were sprayed May 20, June 
20, and July 17, the first spraying being about a month 
after blooming, the second just after picking. 




Fig. 52. 



•Brown rot (sclerotiniose) showing various stages of decay. 
After Clinton. 



Rust. See peach. 

Black knot (Plowrightia morbosa (Schw.) Sacc). — As 
upon the plum, this knot causes serious injury to the cherry. 
In some sections it has spread to the wild cherry and 
plum trees in such abundance as to render control prac- 
tically impossible, and in this way it has killed the cherry- 
growing industry. Taken in time it is easy to control. 
See plum. 



DRUPACEOUS FRUITS 119 

Brown rot, mold (Sclerotinia fructigena (Pers.) Schrcet.). — 
The same fungus which produces disastrous results upon 
the peach also causes rot of the cherry. Several stages 
of its development are illustrated in Fig. 52. The dis- 
ease is known practically everywhere the cherry is grown, 
and large losses are frequent. Fifty per cent loss was re- 
ported from New York, and 25 per cent from Missouri. 
Treatment is the same as for the peach. 

Yellows. See peach. 

Curl (Exoascus Cerasi FckL). — The cherry curl is closely 
related to that of the peach. The leaves become wrinkled 
before they are full size, and spores are produced on the 
surface of the leaf, as they are in other curls. Instead of 
forming flower buds and spurs, affected regions develop a 
profusion of twigs, " witches' brooms." The disease is 
not common in America; but should it become so, it can 
be held in check by pruning out the diseased twigs. It is 
perennial in the twigs and should be avoided in budding 
and grafting. 

Scab. See peach. 

Powdery mildew (Podosphceria Oxycanthce (DC.) DeBy.). 
— This mildew, described in connection with the apple dis- 
eases, sometimes does damage to the plum and cherry, 
especially on nursery stock, where it prevents either the 
growth of the seedling or successful budding or grafting. 

On old leaves the disease does not cause great damage, 
but when the attack is made on young growing tips, or on 
young leaves, these delicate structures suffer greatly from 
loss of nourishment. 

Contrary to the nature of most fungous diseases the mil- 
dew grows best during fair, dry weather. A light rain, 



120 



DISEASES OF ECONOMIC PLANTS 



which spreads the spores and furnishes moisture enough to 

allow them to germinate, followed by a dry spell, best 

favors the development of this disease. 

The use of the Bordeaux mixture 
has proved very satisfactory. Apply 
about every ten days during the early 
growing season; more frequently if 
necessary to replace any poison 
washed off by the rain. 

Wood rot (Schizophyllum commune 
Fr.). — Small white specks, the sporo- 
phores, appear upon the limbs and 
trunk in early summer. 1 In the au- 
tumn they are well developed and 
abundant; white and very hairy, 1-3 
cm. in diameter, usually attached on 
one side with the margins incurved. 
The gills are white, woolly, branched, 
deeply split along the edge, and 
revolute. 

The affected wood is brittle and 

penetrated by black lines. Apparently this disease starts 

in roots injured by tools during cultivation. 




Fig. 53. — Schizophyllum 
commune, frequently the 
causal fungus of wood rot 
of cherry and other trees. 
After Atkinson. 



PEACH 

Brown rot, mold (Sclerotinia fructigena (Pers.) Schrcet.). 
■ — Probably no other disease is so destructive to peaches, 
plums, and cherries as is the brown rot, which, attacks 
the fruits as they approach maturity, turning them 
brown, soft, and useless. Aside from injuring the mature 

1 Heald, F. D., Neb. Agr. Exp. Sta. Rpt. 19, p. 29. 



DRUPACEOUS FRUTTS 



121 



fruit, it attacks the flowers and twigs. The disease ranges 
over the entire peach-growing territory, and in some years 
the loss has amounted to 50 per cent of the crop or more. 



Hfc vv*fl 


PP1 




BBp *" 11 





Fig. 54. — Two packages of peaches, one healthy, the other affected with brown 
rot (sclerotiniose). After Scott. 



The estimated damage in Ohio alone in one year was a 
quarter of a million dollars ; in one year in Pennsylvania 
twenty carloads were lost. Apples, pears, and quinces are 
attacked, but to lesser extent. 

Its characteristic appearance on the fruit enables one to 



122 



DISEASES OF ECONOMIC PLANTS 



recognize it easily. It first appears as small, circular, brown, 
decayed spots. These rapidly enlarge until they embrace 
the whole fruit, which at the same time shrinks slightly. 
As the decay advances, small tufts of brown threads appear 
near the centers of the original spots, and spread rapidly 
until the whole fruit is covered with them. 

If the fruit hangs in clusters, adjacent fruits begin to 
decay at the points of contact, and the disease spreads from 

fruit to fruit until whole clus- 

4jy^ ters are lost. Fruit, after it 

^^ ^^ is picked, may also succumb 

i\. jfed/r to attack, and peaches tha 

M| were apparently sound at pick- 

Bg^fe ing may be seriously damaged 

jSl when they reach market. Thus 

S f* the loss falls upon grower 

jH mf dealer, and consumer. The 

^^8 BPPF 7 *" decay is so rapid that infection 

* : 1 to-day may mean a totally un 



Fig. 55.— Mummy peach showing salable peach two days hence. 

Sclerotinia ascophores. After t» i v i xi ^ 

Scott Peaches diseased on the tree 

may fall to the ground, or 
remain on the tree, where they shrivel and hang over winter, 
to constitute the " mummy " peaches so familiar in infected 
orchards. 

Upon the blossom the disease is first evident as a slight 
brownish discoloration which spreads rapidly, causing the 
flower to wither and eventually fall off as a rotten mass, 
carrying contagion to everything in its path. This damage 
to the flower is often confounded with frost effects. From 
the flower the rot may spread to adjacent twigs, through 



DRUPACEOUS FRUITS 123 

the flower stalk. Infection of the twigs may also occur 
directly from diseased fruit. 

From repeated observations it seems probable that the 
branches cannot be infected through their unbroken skin, 
or if so, only rarely. Smith 1 states that the examina- 
tion of hundreds of twigs in all stages of disease showed 
that every one was associated with blighted and persistent 
flowers. 

The inroads of this disease are so serious that many 
peach and plum growers have been obliged either to secure 
a remedy for this pest or abandon the crop. Years in 
which there is full fruitage, accompanied by damp, warm 
weather, are almost certain to bring a severe attack. But 
it is not the weather which directly causes the rot ; rather 
it is the fungus which causes the rot when the weather 
gives the proper conditions for the development of the 
fungus. 

\ The mummified fruit that falls to the ground serves as 
the hibernating quarters of the causal fungus. If these 
mummies be carefully observed in the spring, some of 
them will be seen to bear small stalked disks (Fig. 55). 
These are the organs which furnish spores for the following 
spring. 

It follows that any practice which destroys or covers up 
these mummified fruits lessens the spring inf ec tion. Active 
treatment in the form of spraying is also necessary. The 
most successful spray is that employed by Scott, 2 which 
gave the following results: — 

1 Smith, E.F., Jour. Mycol., 7, 37, September, 1891. 

2 Scott, W. M., U.S. Dept. Agr. Bur. Plant Indus. Circ. 27, April, 
1909. 



121 



DI8EA8E8 OF ECONOMIC PLANTS 



Results ok Experiments for the Control ok the Peach 
Brown Rot, Marshallville, (!a., L90S 



Plot 


Treatment 


Pbachei 

am v.< "i BSD with 

Bbowh R<m 


Peaches 
Scabbed 


Peaches 

IIAI>I,V 

Scabbed 


1 
IS 


Lime-sulphur wash (15 10 
r>0), hot water . . . 
Lime-sulphur w;i,sli ( 1 5 L0 

50), Cold water . . . 

( Sheck no treatment . 


Per cent 

L0.56 

12.22 

36.08 


Per cent 

20.75 

L6.60 
93.63 


Per cent 
O.SO 
0.00 

42.12 



The treatment recommended by Scott for brown rot and 
scab bused upon these results is us follows: For the com- 
bined treatment of peach scab and brown rot, at least three 
applications of the self-boiled lime-sulphur wash are 
necessary, " the first, three to four weeks after the petals 
drop, the last about a month before the fruit ripens, and the 
second midway between. Scab infection begins four to 

six weeks after the trees bloom, and in order to 

control this disease the first treatment must be made not 
Infer than a month after the petals drop. The time of the 
last application must be determined by the ripening date of 
the variety. To avoid staining the fruit the last spraying 
should be made a month before the fruit ripens, though a 
later treatment would be more effective against the brown 
rot. Three applications distributed in this manner are 
sufficient for the Elberta and earlier varieties. A fourth 
treatment will doubtless often be desirable for later matur- 
ing varieties. 
l( There seems to be no question as to the advisability of 



DBUPACEOUS FBUIT8 L25 

spraying the peach orchard where the brown rot and scab 
are troublesome, but many disappointments are naturally 
to be expected. The curculio and other insects readily 
break the skin of the peach and admit the brown-rot, fungus 
even through a coating of the spray mixture, so that a cer- 
tain amount of rot may always be expected when the condi- 
tions are favorable." 

Scab (Cladosporium carpophilum Thuem.). — Thisdisease, 
which is widespread and so common that many people regard 





Fia. 56. — Peach Noub. Original. 

it as an integral part of the peach, may consist of isolated, 
sooty, black specks, or of black specks so numerous as to 
coalesce into large blotches. These sometimes cover as 
much as one third or one half of the peach. The side which 
is attacked is dwarfed, often cracked, and the flesh adjacent 
to the diseased part is bitter and gnum, even after the normal 
portions are ripe. 

The disease develops in most serious form during rainy 
seasons, and is worse upon some varieties than upon others. 
It is especially bad upon Hill's Chili. It is reported from 
Missouri to have done damage equal to 70 per cent of the 



126 



DISEASES OF ECONOMIC PLANTS 



value of the crop, and Selby estimated the loss in one crop in 
Ohio at from 20 to 50 per cent. 
The beneficial effects of the self-boiled lime-sulphur 




Fig. 57. — Peach leaf curl. After Atkinson. 



treatment, and the method of using it, have been given 
under peach brown rot. 

Curl (Exoascus deformans (Berk.) Fckl.). — Throughout 
the peach-producing region this disease abounds, it being 
particularly injurious in the more moist localities. The 
annual loss caused by it approximates $3,000,000 in the 
United States. 

The disease is due to a fungus which grows in the leaves, 
causing the peculiar malformation which justly gives rise 



DRUPACEOUS FRUITS 127 

to the popular name of curl. This fungus destroys the 
utility of the leaf as a starch-producing organ, and even- 
tually causes defoliation, and thus direct loss to the trees. 
This loss may be manifest in two ways : first, by the pres- 
ent effect upon the vitality and vigor of the tree, and im- 
mediate injury to the crop; second, by a weakening of the 
tree in succeeding years, due to the lack of full nourishment 
during the period of attack. The injury in the present 
year, manifest by a loss in productiveness, is obvious to the 
grower. The injury in succeeding years, often fully as 
great, is frequently overlooked, or is not attributed to its 
true cause. 

It was formerly thought that this fungus persisted in the 
twigs over winter, and thus lurked ready to infect the new 
leaves as they began to develop. It has, however, been 
proved that nearly, if not quite, all spring infection is due, 
not to perennial mycelium, but to spores which remain on 
the bark of the trees. 

Prevention of the disorder lies in killing these spores of 
the fungus by winter spraying. For this purpose Bordeaux 
mixture, the lime-sulphur, or a simple copper sulphate 
solution is efficient. In many ways the Bordeaux is more 
satisfactory than the copper sulphate solution. It does not 
have as strong corrosive action upon the pump. It is easily 
seen upon the trees, and consequently it is not difficult to 
determine when a thorough application has been made. 
There is probably little choice between these two solutions 
on the ground of efficiency. The lime-sulphur is preferable 
when insects also are to be met. The spraying should be 
made from one to three weeks before the buds open in the 
spring, and thoroughness is the chief point desired. Spray- 



128 DISEASES OF ECONOMIC PLANTS 

ing should be clone in dry calm weather, during the middle 
of the day, in order to avoid dew or frost upon the limbs. 

Pierce l states that as a result of treatment of the peach 
curl, in California, from 95 to 98 per cent of the spring 
foliage was saved. A net gain of 600 per cent in the 
foliage over that retained by adjoining unsprayed trees 
resulted in the case of several different sprays. The Bor- 
deaux mixture, when applied to the dormant tree, increased 
the weight and starch-producing power of the leaves, and the 
sprayed trees showed great gain over the unsprayed in the 
number and quality of the fruit buds which they produced 
for the following year. The gain in the number of spur 
buds was over 100 per cent in some cases. The sprayed 
trees also produced more vigorous growth of new wood, 
the wood to produce the crop for the next year. Thus, in 
one experiment the spring growth of the unsprayed tree 
averaged 7.85 inches; on the sprayed trees it was 24.75 
inches. The average value of fruit, per tree, in rows 
treated with the most effective Bordeaux mixture ranged 
as high as $6.20 above that in adjoining untreated rows, 
or the equivalent of a net gain of $427.80 per acre. Over 
one thousand per cent net gain in the set fruit has resulted 
from the use of some of the more effective sprays. 

The trees should be sprayed each season, since experi- 
ments prove that treatment one season will not prevent the 
disease the following year. Spraying should be done even 
though the trees are not expected to bear, since the lqss of 
the crop of leaves is as great a drain upon the trees as is the 
maturing of one half to two thirds of a crop of fruit. 

1 Pierce, N. B., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 20, 
1900. 



DRUPACEOUS FRUITS 129 

Die back (Valsa leucostoma (Pers.) Fr.). — This disease 
of limbs, trunk, and twigs is serious in Europe and Australia. 
It was first described in the United States by Rolfs of 
Missouri in 1907/ who noted it upon peach and Japanese 
plum. 

Infection occurs upon buds or wounds during the growing 
season, and in early winter and spring the tips of young 
branches, especially water sprouts, are killed back from 2.5 
to 46 cm. As many as 300 such dead twigs have been 
noted on a single tree. It develops most rapidly in a 
warm spell following freezing weather in the spring, and is 
more serious upon trees which have been weakened by 
any cause. 

Twigs killed during the winter show at first a dark, pur- 
plish skin, changing later to leathery, scarlet, or purple, 
finally drab. Then the skin loosens and wrinkles. At this 
time black pycnidia appear under the skin. These soon 
push out a white cap through a transverse slit in the skin, 
and in wet weather exude very fine red threads of spores. 
Gum flow usually accompanies the constriction, marking 
the juncture of dead and healthy wood. During summer, 
leaves on infected twigs frequently wilt, owing to the gir- 
dling of the stem. Upon the trunks large wounds, often 
regarded as sun scalds, are produced, while upon young 
limbs the wounds appear as enlargements or " knots." 
Large limbs or even whole trees succumb. 

Excision should be practiced. 

Blight, shot hole (Coryneum Beyerinkii Oud.). — This 
disease, which has been troublesome in California for 
years, often destroying the crop and weakening the trees, 

1 Rolfs, F. M., Sci. n. s. 26, 87. 



130 DISEASES OF ECONOMIC PLANTS 

was first noted by Pierce, 1 and has been fully described by 
Smith. 2 

It consists in dying of the buds of fruiting wood, spotting 
of green twigs, and dropping or underdevelopment of young 
leaves and fruit, accompanied by gummy exudate, especially 
upon the one-year-old fruiting twigs. Leaves opening from 
buds which survive the disease are marked by small dead 
areas of tissue, which soon fall out, leaving " shot holes.'' 
It is essentially a winter or early spring disease of fruiting 
twigs and one-year-old wood, and the principal damage is 
from death of buds and twigs before the fruit develops. 
Infection occurs in winter before new growth begins. 

By pruning, then sprajdng with the Bordeaux mixture or 
other cleansing spray, during the early winter (in California 
between November 1 and December 15), the best results 
are obtained. 

Crown gall (Pseudomonas tumefaciens E. F. Smith & 
Townsend). — Crown gall consists in a swelling, a tumor-like 
outgrowth, near the ground line on certain trees and shrubs, 
particularly upon members of the rose family, pomes, drupes, 
raspberries, etc. Careful cross inoculations by. Hedgcock, 3 
using fragments of galls, have demonstrated that crown 
gall of the almond, apricot, blackberry, cherry, peach, plum, 
prune, chestnut, and walnut are inter communicable. It 
has also been demonstrated by Smith and Townsend that 
crown gall of the peach tree as well as of tomato, po- 
tato, tobacco, beet, hop, carnation, grape, raspberry, and 

fierce, N. B., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 20, 
p. 179, 1900, and Sci. n. s. 25, 305, February, 1907. 

2 Smith, R. E., Cal. Agr. Exp. Sta. Bui. 191, p. 93, September, 1907. 

3 Hedgcock, G. G., U.S. Dept. Agr. Bur. Plant Indus. Bui. 131. 



DRUPACEOUS FRUITS 



131 




Fig. 58. — Peach crown gall. After Hedgcock. 

apple x can be produced by inoculation with Pseudomonas 
tumefaciens, also that the organisms of the peach, apple, 
hop, rose, and chestnut galls are interchangeable. It is 



1 Hedgcock, G. G., Sci. n. s. 25, 671, April, 1907, and Sci- n. s. 29, 273. 



132 DISEASES OF ECONOMIC PLANTS 

probable, therefore, that at least one cause of crown gall 
is the organism mentioned. 

All diseased stock should be avoided, as well as stock from 
nurseries where the disease is known to exist. 

Bacteriose (Bacterium pruni E. F. Smith 1 ). — A "shot 
hole " disease of peach leaves, which causes prema- 
ture defoliation, is attributed by Smith and by Rorer 2 to 
bacteria. The disease has been found 
during several years in different states 
and is believed to constitute one of the 
most common of the " shot-hole " dis- 
eases in the South and Middle West. 
The fruit and twigs are also affected. 
Upon the leaf it appears as somewhat 
angular purplish brown spots, 2-5 mm. 
FlG- 59. —Mildew upon in diameter, which may coalesce and in- 
peach fruit. After V olve large areas. Upon twigs it kills 
the bark, forming purplish black sunken 
areas, 2-3 mm. wide, which may extend to 3-8 cm. in length, 
and even girdle the twig and kill the shoot. Infection is 
most frequent at a leaf scar. Upon the fruit small pur- 
plish spots appear. Over these the skin soon cracks. The 
Elberta is especially susceptible. No effective treatment 
has yet been demonstrated. 

Powdery mildew, podosphaeriose (Podosphceria Oxycanthce 
(DC.) DeBy.). — This widespread mildew is in general ap- 
pearance very similar to the powdery mildew of the grape- 
cherry, lilac, and rose, etc. It sometimes becomes so abun- 

1 Smith, E. F., Sci. n. s. 17, 456, and Bacteria in Relation to Plant Dis- 
ease, I, Figs. 11, 15, 70, 71, 72, and PI. 19. 

2 Rorer, J. B., Mycologia 1, 23, January, 1909, and Sci. n. s. 30, 224. 




DRUPACEOUS FRUITS 133 

dant as to almost completely ruin the crop, by attacking 
the leaf, fruit, and twig. When on the fruit, it appears first 
while the peach is small, causing irregular, grayish, moldy 
blotches. As these enlarge, cracks often develop. 

The winter cleansing sprays recommended for the peach 
curl are effective in killing wintering spores, and thus largely 
diminish the injury from this pest. 

Powdery mildew, sphaerothecose (Sphcerotheca pannosa 
(Wallr.) Lev.). — This powdery mildew, in general appear- 
ance like podosphseria, sometimes interferes with the growth 
of leaves and young twigs and stunts the trees. For treat- 
ment, see podosphseriose. 

Frosty mildew (Cercosporella Persica Sacc). — In damp, 
shaded localities, especially on trees of dense foliage, a 
disease occurs in the form of pale yellowish leaf spots. 
These show, on the underside, a delicate frostlike appear- 
ance, due to the growth of white spore-bearing hyphse. 
It is not usually serious, though widespread, and the 
treatments recommended for the other diseases will suf- 
fice to hold this disease in check also. 

Texas root rot. See cotton. 

Shot hole, cercosporose (Cercospora circumscissa Sacc). 

— This is very widespread, producing spots, or, when the 
diseased tissue falls out, oval holes, in the leaves. It also 
infects small branches. The chief injury lies in destruction 
of leaf tissue and of valuable shoots. 

The dormant spraying recommended for the curl is useful 
here. 

Shot hole, phyllostictose (Phyllosticta circumscissa Cke.). 

— This is similar in appearance and treatment to cercospo- 
rellose. 



134 DISEASES OF ECONOMIC PLANTS 

Pustular spot (Helminihosporium carpophilum Lev.). — 
Peaches with this disease are described by Selby 1 as 
" Badly disfigured, having numerous pimply red spots with 
light brown centers." The peach, in an earlier condition of 
the disease, shows small rusty brown spots upon its upper 
side. These spots increase in size and develop light brown 
centers, 1-2 mm. in diameter. Upon yellow varieties the 
pustule is commonly lacking, there being but a light brown 
center with a red border. 

As the fungus which causes this spot rests purely upon 
the surface its development may be prevented by spraying. 
Selby 2 reduced the injury from 16 per cent to 1 per cent by 
three applications of the Bordeaux mixture. 

Rust (Puccinia Pruni-spinosce Pers.). — A true rust exists 
parasitically upon the peach and its relatives, the plum 
and cherry. While more common upon the plum, it very 
frequently does damage to the peach, in some cases being so 
serious as to cause almost complete defoliation. The alter- 
nate stage is not uncommon upon the hepatica in the spring. 

This malady will be recognized by the presence of small, 
round, dusty sori on the lower surface of the leaves and on 
the young shoots, while in the immediate region of these 
spore-bearing pustules the leaf, seen from above, often 
presents a reddish or reddish yellow color. 

Reliance must be placed upon a cleansing spray such as 
is recommended for the peach curl, to lessen the effect of the 
attack of the rust. 

Stem blight, phomose (Phoma Persicce Sacc). — A fungus 
on the bark which fructifies in minute pustules sometimes 

1 Selby, A. D., Ohio Agr. Ex. Sta. Bui. 92. 

2 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 92. 



DRUPACEOUS FRUITS 135 

causes twigs to die. The disease may be readily recog- 
nized by the dead bark thickly studded with small pyc- 
nidia. Burning of the diseased branches will prevent the 
spread of the pest. 

Yellows. — The peach yellows has been known in the 
United States something like a hundred years. From a 
region near Philadelphia, as a center, it has spread until 
now it is known throughout a large territory and is con- 
stantly extending its frontier in every direction. The 
disease is of unknown cause, but it has been proved beyond 
question that it is contagious. The roots of diseased 
plants, however, do not infect the soil, and trees may safely 
be set in the places from which diseased trees have been 
removed. 

Recognition marks, which leave no uncertainty as to its 
identity, are described by Smith 1 as follows: " Prematurely 
ripe, red-spotted fruits, and premature unfolding of the 
leaf buds into slender, pale shoots, or into branched, broom- 
like growths, are the most characteristic symptoms of yel- 
lows. The time of ripening of premature fruit varies 
within wide limits; sometimes it precedes the normal 
ripening by only a few days, and at other times by several 
weeks. The red spots occur in the flesh as well as on the 
skin, making the peach more highly colored than is natural. 
The taste of the fruit is generally inferior and often insipid, 
mawkish, or bitter. Often this premature ripening is the 
first symptom of yellows. The peaches are then of good 
size and quite showy, and occur on trees in full vigor, upon 
limbs bearing abundant green foliage, and sometimes also 
other fruits which afterwards ripen normally. 

1 Smith, E. F., U.S. Dept. Agr. Farmers' Bui. 17, p. 7, 1894. 




Fig. 60. — Peach tree showing yellows. After Sheldon. 



DRUPACEOUS FRUITS 137 

" Often during the first year of the disease this kind of fruit 
is restricted to certain limbs, or even to single twigs, which, 
however, do not differ in appearance from other limbs of the 
tree. The following year a larger part of the tree becomes 
affected and finally the whole of it, the parts first attacked 
now showing additional symptoms, if they have not already 
done so. These symptoms are the development of the 
winter buds out of their proper season. Like the prematur- 
ing of the fruit, the date of this also varies within wide 
limits. The buds may push into shoots only a few days 
in advance of the proper time in the spring, or may begin 
to grow in early summer, soon after they are formed, and 
while the leaves on the parent stem are still bright green. 
This is a very common and characteristic symptom, and is 
especially noticeable in autumn when the normal foliage 
has fallen. Usually under the influence of this disease 
feeble shoots also appear in considerable numbers on the 
trunk and main limbs. These arise from old resting buds, 
which are buried deep in the bark and wood, and remain 
dormant in healthy trees. Such shoots are sometimes un- 
branched, and nearly colorless, but the majority are green 
and repeatedly branched, making a sort of broomlike, 
erect, pale green, slender growth, filling the interior of the 
tree." 

A tree exhibiting these symptoms should be cut and 
burned. It is valueless, and its presence is a serious menace 
to the owner as well as to the state at large. 

Rosette. — The peach rosette is southern in distribu- 
tion, being known principally in Georgia, South Carolina, 
and Kansas. As to its nature, means of spread and of 
prevention, precisely what has been said of yellows ap- 



138 DISEASES OF ECONOMIC PLANTS 

plies. Its distinguishing characters are given by Smith as 
follows : 1 — 

" Rosette clearly belongs to the same type of diseases as 
yellows, but its first stages are more striking and its prog- 
ress is much more rapid. It may first attack part of the 
tree and then the remainder, the same as the yellows, but 
it is more likely to appear at once on the whole tree, and 
generally in early spring. In trees attacked in this manner, 
all of the leaf buds grow into compact tufts or rosettes. 
These rosettes, though seldom more than two or three 
inches long, usually contain several hundred small leaves. 
A tree thus attacked always dies during the following winter 
or autumn. When part of a tree is thus attacked, that 
part dies as above described, and the remainder shows 
symptoms the next spring, to die in turn after about six 
months. 

" The prevailing color of the foliage is yellowish green or 
olivaceous. The older leaves at the base of the tufts are 
largest, and frequently grow to a length of several inches, 
but have inrolled margins and a peculiar stiff appearance, 
due to the fact that they are straighter than healthy leaves. 
These outer leaves turn yellow in early summer and drop 
as readily as though it were autumn, while the inner leaves 
of the rosette are still green and delicate. The compact 
bunching of the leaves is very conspicuous, and makes the 
trees look quite unlike those affected by yellows. Where 
a tree is attacked in all parts, it matures no fruit. In all the 
cases which have been noticed the fruit borne by affected 
trees either shrivels while green and drops off, or else ripens 
naturally. 

1 Smith, E. F., U.S. Dept. Agr. Farmers' Bui. 17, p. 14. 



DRUPACEOUS FRUITS 139 

" In the absence of premature, red-spotted fruit, in the 
severity of the disease from the outset, and in its rapid 
progress, it is quite unlike yellows, which is decidedly 
chronic, and the first slight symptoms of which usually 
occur in very green and thrifty trees, and are frequently 
overlooked the first season." 

The treatment is to cut and burn. No carelessness 
should be tolerated as regards this disease or yellows. 

Little peach. — This seems first to have been publicly 
noted by Smith in an address in Michigan in 1898/ in which 
state it had been of alarming character prior to 1893; since 
these years it has appeared in New York and New Jersey. 
The most prominent symptom is that the fruit remains 
small, one half to one third the usual diameter, and ripens 
some 10 to 14 days later than normal fruit, and then with 
insipid or bitter flavor and " stringy " flesh. The leaves 
are small, one half normal size, and vary from light green 
to yellowish green, and droop somewhat. An orchard once 
affected is of nor further value, 2 and should be removed 
and burned because of the possible danger to other trees 
that their presence creates. 

PLUM 

Black knot (Plowrightia morbosa (Schw.) Sacc). — The 
black knot receives its name from the swollen black distor- 
tions, 3-15 cm. long, upon the branches. In a young con- 
dition the galls are olivaceous, but as the season advances 
they become darker and eventually coal black. At the 
same time the texture changes from soft to hard and brittle. 

1 Smith, E. F., Fenville (Mich.) Herald, October 15, 1898. 

2 Blake, M. A., N.J. Agr. Exp. Sta. Bui. 226, p. 10, January, 1910. 



140 



DISEASES OF ECONOMIC PLANTS 



When the disease extends completely around the twig, 
the supply of nourishment to more distant parts is seriously 

interfered with. If 
less than the whole of 
the circumference be 
involved, the damage 
is not so great, but it 
is even then sufficient 
to very seriously im- 
pair the fruiting of 
the tree. Black knot 
may either kill the 
tree in a year or two, 
or simply destroy its 
value. All varieties 
of plums and nearly 
all cherries are sub- 
ject to the disease, 
which is therefore 
very widely distrib- 
uted. 

It is probable that 
infection can occur 
only through injured 
bark. One step to- 
wards lessening the 

Fig. 61. — Portion of a plum tree badly infested v ,-i . <■ 

with black knot, original. dlsease * s therefore 

to exercise all care 
not to bruise the tree. Effective measures, however, must 
consist of pruning out and burning all black knots. This 
course, if followed persistently and thoroughly, will remove 




DRUPACEOUS FRUITS 141 

all danger. Experiments show that spraying very materi- 
ally lessens the spread of the black knot, and while it might 
not pay to spray to prevent this disease, spraying in an 
orchard for other reasons really diminishes this danger. 

Plum pockets (Exoascus Pruni Fckl.). — The name " plum 
pocket," or " plum bladder," arises from the curious hollow 
deformity of the plum, caused by a fungus. The pulp and 
stone of the fruit are replaced by a thin, soft, inflated shell, 
and in place of the seed merely a hollow cavity exists. 

The disease appears soon after the flowers fall. The 
affected fruits vary in size from 2-5 cm. in length, and can 
be readily distinguished from the healthy fruit by their 
pale yellow color. As they age, they become coated over 
with a fine powder, consisting of the spores of the fungus 
which caused the malformation. Later the pockets turn 
black and fall. 

The- disease is local in character. A single tree in an 
orchard may bear " pockets," sometimes every fruit on the 
tree being affected, while surrounding trees are normal. 
A tree once affected continues to bear pockets in succeeding 
years. Treatment consists in cutting and burning the 
affected branches or trees. 

Leaf spot (Cylindrosporium Padi Karst) . — The leaf spot 
or shot-hole disease attacks plums and cherries, causing 
a portion of the leaf tissue to become discolored, the spot 
often bearing a red or purple border. If abundant several 
spots may coalesce as they enlarge. The tissue involved 
dies, turns brown, and eventually drops from the leaf, 
leaving circular or ragged holes. This character gives rise 
to the common name " shot-hole disease." The disease 
is also frequent upon petioles. 



142 DISEASES OF ECONOMIC PLANTS 

The attack is very insidious, and the disease often does 
much damage before its presence is really known. Defoli- 
ation is the chief injury, the leaves falling freely after the 
attack of the fungus. This checks starch production, and 
thus impairs the tree's general vigor and productiveness, 
even weakening the tree to such an extent that it cannot 
withstand the winter. As high as 80 per cent damage has 
been reported. The loss in Ohio was estimated as $20,000 
in one year. 

The disease is especially injurious to nursery stock, as it 
may interfere with successful budding and grafting. The 
following recommendation in the way of treatment is 
made : x — 

1. Apply the Bordeaux mixture about ten days after 
the blossoms fall. 

2. About three weeks later repeat this treatment. 

3. About four weeks later repeat again. 
See also treatment for cherry. 

In one instance, in the New York Station, " The treat- 
ment resulted in an average increase per tree of twenty- 
four and one half pounds of marketable fruit, at an 
estimated cost of less than one cent per pound. The 
average yield per tree of picked fruit was increased 44 
per cent, the marketable drops increased 8 per cent, and 
the waste was decreased 81 per cent. The total yield of 
marketable fruit, as recorded in pounds, was 45 per cent 
greater when the trees were sprayed than when they were 
not sprayed." 

Scab (Cladosporium carpophilum Thuem.). — The plum 
scab consists of spots on the fruit similar to the scab 

1 Beach, S. A., N.Y. (Geneva) Agr. Exp. Sta. Rpt. 15, p. 399, 1896. 



DRUPACEOUS FRUITS 143 

of peaches. When plums begin to ripen or are just turn- 
ing in color, small round patches, pale greenish or gray- 
ish in color and not larger than the head of a pin, 
appear. These increase in size, in some cases to a centi- 
meter across. In older specimens the diseased spots are 
frequently confluent and of darker brown color. In very 
old specimens, especially where the fruit has undergone 
decomposition, the patches become black and uneven. 

Treatment identical with that recommended for the 
peach scab will apply in this case. 

Blight (Bacillus amylovorus (Burr.) De Toni). — The 
blight of the apple and pear have been discussed on 
preceding pages. A very similar blight is rarely known 1 
to affect the plum tree, and careful studies by Jones 2 show 
that the diseases on plum and, pear are identical. While 
the plum blight is exceedingly rare, it is important that 
fruit growers should recognize that the disease is identical 
with pear blight, since this knowledge will help very ma- 
terially in its control. 

For treatment see pear. 

Yellows. See peach. 

Brown rot (Sclerotinia fructigena (Pers.) Schrcet.). — 
Brown rot is very serious with the plum as it is with the 
peach and cherry. The loss in Ohio in one year was esti- 
mated at $25,000. 

For description and treatment see peach. 

Powdery mildew, podosphaeriose. See cherry. 

Rust (Puccinia Pruni-spinosce Pers.). — The rust of the 

1 Whetzel, H. H., & Stewart, V. B., N.Y. (Cornell) Agr. Exp. Sta. Bui. 
272. 

2 Jones, L. R., Gentrbl. f. Bakt. Parasitenk. u. Infek. 2 (Abt. II), 825. 



144 DISEASES OF ECONOMIC PLANTS 

plum, like that of the peach, usually causes but slight in- 
jury. See peach. 

Root rot, armillariose. See p. 173. 

Bacteriose. See peach. 

Die back, valsose. See peach. 



SMALL FRUITS 
BLACKBERRY 

Leaf spot (Septoria rubi Westd.). — Upon the leaves 
of blackberries, raspberries, and dewberries small spots 
frequently appear, having a central region white or ashen 
in color, and the border brown or often of reddish tint. 
These spots are about 3 mm. in diameter. Close examina- 
tion of the central ashen region, especially with a hand 
lens, reveals exceedingly small, black pycnidia scattered 
throughout. 

While this disease is exceedingly common and of wide 
distribution, it does not often develop an epidemic and 
usually does but little injury, though its damage has been 
estimated as high as 20 per cent in Florida and Ohio. No 
treatment has yet proved of sufficient value to warrant 
its use. 

Anthracnose (Glceosporium venetwn Speg.). — The an- 
thracnose is one of the most serious diseases of this crop. 
For description and treatment see raspberry. 

Crown gall. See raspberry. 

Orange rust (Gymnoconia inter stitialis (Schlecht) Lagh.) 
— In the early spring the under sides of the leaves of black- 
berries and raspberries often present a livid red or orange 
color. On walking through a region so affected the shoes 



SMALL FRUITS 145 

become coated with a reddish dust, shaken from the dis- 
eased leaves. This rust was observed as early as 1817, 
in Kamchatka, and is very widely distributed in the United 
States, Europe, and Asia, upon some nine species of Rubus, 
both cultivated and wild. It is known from Maine to 
Minnesota and Florida to California, and is in some cases 
very destructive. 

Examination of a diseased plant shows that its growth 
has been much retarded by the fungus ; the leaves are 
curled, distorted, unusually small, and lacking in green 
color. Plants so affected never recover, and are useless. 
Preceding by some two or three weeks the conspicuous red 
rust above referred to occurs another stage of the disease 
that is often overlooked. This consists of a thick growth of 
small columnar, glandlike structures, chiefly upon the 
upper side of the leaf, and present even before the leaves un- 
fold. These structures (spermagonia) become more distinct 
as the leaves enlarge. 

The mycelium of the causal fungus when once established 
in the cane lives in it from year to year, spreading through- 
out the plant. Spraying is therefore useless. In fact the 
only successful way of combating this disease is to remove 
and burn all affected plants. Diseased plants are valueless 
and are a menace to the healthy plants. 

Late rust (Kuehneola albida (Kiihn.) Magn.). — As 
the name implies, this rust usually appears late in the 
season, this distinguishing it from the red rust, which is 
most abundant in the spring. The spores are not so abun- 
dant as those of the red rust, but occur in small, pale yellow 
or whitish spots scattered on the underside of the leaf. 
This disease has not as yet been sufficiently prevalent to 



146 



DISEASES OF ECONOMIC PLANTS 



be of serious import, although its increase at any time under 
favorable climatic conditions may place it among the im- 
portant plant enemies. 



CRANBERRY * 



Scald, blast (Guignardia Vaccinii Shear). — The fruits 
are attacked as soon as the blossom falls, or even the 




Fig. 62. — Cranberry scald and blast. After Shear. 



blossom itself may be blighted. The affected berry 
shrivels, turns black, and is covered with pycnidia. 
From such fruits the disease spreads to other fruits and 
to the leaves. In some bogs as much as 50 per cent of the 
crop is thus destroyed. This form of disease is commonly 

1 The information given here is taken largely from Shear, C. L., U.S. 
Dept. Agr. Bur. Plant Indus. Bui. 110, and Halsted, B. D., N.J. Agr. Exp. 
Sta. Bui. 64. 



SMALL FRUITS 147 

designated as the " blast," while still another form of it 
has been termed the " scald." 

The scald may appear upon the berries, causing small, 
light-colored, softened, watery spots. These rapidly in- 
crease in circumference, and even envelop the whole fruit. 
Sometimes the diseased portion shows more or less distinct 
brownish zones. In other cases the zones are lacking, 
and the whole fruit becomes very soft and of light, watery 
color. 

Upon the leaves irregular reddish brown spots with 
pycnidia are more rarely produced. 

Plants after several years of disease die, as do also cut- 
tings during the first or second year after planting. 
Thrifty plants resist the disease much more than weak 
plants. Particular attention should therefore be given 
to provide such irrigation as to best favor the health and 
vigor of the plants. Sanding the fields often gives good 
results, doubtless partly removing contagion by covering 
infective material. It is also advisable for the same end to 
rake out and burn all dead and infected plants in the au- 
tumn. Cuttings should be taken from such plants as show 
resistance to the disease. 

In spraying experiments by Shear * five applications of 
6-6-50 Bordeaux mixture, with 4 pounds of resin-fish oil 
soap added to increase adhering power, showed 2.36 per 
cent of rotten berries, while the unsprayed plats showed 
92.6 per cent of rotten berries. The cost of application 
was $15 to $20 per acre, using 200 gallons of mixture at 
each application. 

Rot (Acanthorhynchus Vaccinii Shear). — An ef- 

1 Shear, C. L., U.S. Dept. Agr. Bur. Plant Indus. Bui. 110. 



148 DISEASES OF ECONOMIC PLANTS 

feet upon the berry very similar to that of the scald 
fungus appears first as small, light-colored, soft spots, which 
soon destroy the whole berry. Later small, dark-colored 
blotches show under the skin, but no pyenidia appear. 
The disease is found in New Jersey, West Virginia, Mis- 
sissippi, Wisconsin, and Nova Scotia. In importance it is 
the second cranberry disease. 

The treatment suggested for the scald is also effective 
against this rot. 

Anthracnose (Glomerella rufomaculans (Berk.) Spaul. 
& von Schrenk; Vaccinii Shear). — This is less injurious 
than the rot or scald in New Jersey, but is more common 
in Massachusetts and New England. The treatments 
already suggested apply. 

The three diseases just considered cannot well be dis- 
tinguished except by microscopic examination. In some 
cases the berry is soft and light colored, but if the fungus 
develops slowly, the sick portion is not so soft. To 
control them the water supply should be regulated so as 
to avoid great fluctuations during the growing season. 
Too little water is more to be avoided than too much. 
Vines dead from disease should be pulled and burned. 
Bordeaux mixture, at fourteen-day intervals, as suggested 
above, is recommended. 

Hypertrophy (Exobasidium Oxycocci Rostr.). — Hyper- 
trophy is known only in Massachusetts, where in 1906 it 
did considerable damage in some bogs. 

In this disease the buds in the leaf axils, which normally 
remain dormant, grow out into short shoots bearing swollen 
enlarged leaves of pink or light rose color. This character 
has given rise to the name " false blossoms." 






SMALL FRUITS 149 

The disease usually appears before blossoming, and by 
sapping the vigor of the vine prevents fruiting. No treat- 
ment is known. 

Sclerotiniose (Sclerotinia Oxy cocci Wor.). — Just as the 
plants begin to blossom the tips of green shoots first 
show this disease by withering. Then a thin, soft, white 
moldlike outgrowth appears upon the stem and leaves. 
From here the spores spread to the open blossoms and 
infect the young fruit. No further evidence of the disease 
is seen until the berry is nearly mature, when the affected 
berries are found to be full of a cottonlike growth, the 
fungous mycelium. At harvest time such berries show a 
grayish, wrinkled spot, and later the whole berry becomes 
gray, shriveled, and often spotted with dark brown masses 
which break through the skin. Such berries carry the 
disease over winter. 

The destruction by fire of all diseased fruit will lessen 
the evil in succeeding seasons. 

Gall (Synchytrium Vaccinii Thomas). — The cranberry 
gall though not widely known has been serious in some 
bogs, and on account of its rapid spread may become of 
much import in any bog to which it gains entrance. The 
first collection of the disease in America was by Halsted 1 
in New Jersey in 1886. 

It is found upon the leaves, stems, flowers, and fruit as 
small, 0.8-1 mm., red galls which occur in such abundance 
upon the affected part as to cause marked distortion. 

The disease is known to recur year after year, resulting 
in almost complete loss of the crop in infected portions of 
the bogs. 

1 Halsted, B. D., N.J. Agr. Exp. Sta. Bui. 64, December, 1889. 



150 DISEASES OF ECONOMIC PLANTS 

Other plants upon which the same disease occurs are: 
Azalea (Rhododendron viscosum Torr.); sheep laurel, or 
lambkill (Kalmia angustifolia L.) ; sweet pepper bush, 
or white alder (Clethra alnifolid L.) ; leather leaf (Cas- 
sandra calyculata Don.); huckleberry (Gaylussacia resi- 
nosa T. & G.) ; the teaberry, or wintergreen (Gauliheria 
procumbens L.). 

Burning of the infected areas is recommended. 

Fly speck (Leptothyrium Pomi (Mont. & Fr.) Sacc). — 
Fly speck is identical in character with that described for 
the apple. 

CURRANT 

Knot (Pleonectria Berolinensis Sacc). — This disease was 
described by Durand x in 1897 as prevalent in some regions 
of New York State. It has since been found in several 
other states and may be expected wherever currants are 
grown. 

The first symptom is wilting of the foliage, which soon 
turns yellow, dries up, and falls away. The diseased clus- 
ters of fruit are smaller than normal, color prematurely, 
and fall with the foliage, leaving only the bare stalks, which 
soon die. Cuttings made from the apparently healthy 
bushes in a diseased field usually grow slowly, which 
seems to indicate that the fungus causing the disease 
is present in even those stalks which appear healthy. 
After the death of a stalk small, wartlike, sporiferous tuber- 
cles appear in great number upon its surface. 

Cuttings should not be taken from diseased fields. 

1 Durand, E. J., N.Y. (Corneal) Agr. Exp. Sta. Bui. 125, February 
1897. 



SMALL FRUITS 



151 



Here even the ap- 
parently healthy 
plants may be af- 
fected. After the 
disease has once 
gained access to a 
field, all diseased 
plants should be 
pulled and burned 
as soon as they 
are recognized, 
and the soil should 
be allowed to rest 
some years before 
again putting 
either currants or 
gooseberries upon 
it. 

Cane blight 
{Fungus indet.). — 
A sudden wilt of 
the leaves on one 
or more canes in a 
bush is the first 
symptom of dis- 
ease. The entire 
bush may suc- 
cumb, but not usu- 
ally during the first season. Upon splitting the stems 
a discoloration of the bark and wood near the base is 
noticed. This disease, while similar in many of its symp- 




Fig. 63. — Diseased currant canes ; a, Tubercularia 
b, Nectria ; c, Pleonectria. After Durand. 



152 



DISEASES OF ECONOMIC PLANTS 



toms to the knot, may be distinguished from it by the 
absence of wartlike growths upon the surface of affected 
twigs. 

As an effective measure all diseased canes may be cut out 
and burned, cutting well below the diseased area. 




Fig. 64. — Currant leaf spot (septoriose). After Stewart and Eustace. 



Septoriose 
Cercosporose 



The leaf spots 



(Septoria Ribis Desm.) 
(Cercospora angulata Wint.) 



The " currant leaf spot " is a term applied to a peculiar 
spotting of the leaves of both currants and gooseberries. 
It is likely to occur wherever these plants are grown. The 
spot is of rather characteristic appearance, usually circular, 



SMALL FBUITS 



153 



although sometimes irregular in outline, generally about 
3 mm. in diameter. In the center of the brown or gray 
discolored area very minute pycnidia may be seen in the 
case of septoriose; hyphse in the case of cercosporose. 
Defoliation, often serious to the plant, results. 




Fig. 65. — Currant anthracnose. After Stewart and Eustace. 

The Bordeaux mixture is far superior to ammoniacal 
copper carbonate for these diseases. Five applications at 
ten- to fourteen-day intervals are needed, beginning as soon 
as the leaves are open. 

Anthracnose (Pseudopeziza Ribis Kleb.). — The leaves, 
fruit stalks, berries, and canes are affected. Usually 
the disease is not present to great extent, but a few 
serious outbreaks have occurred, notably in central New 
York and in the Hudson River region. It has also been 
noted in Ohio, Iowa, New Jersey, and is probably often 
present to a slight extent in a number of other states. 



154 



DISEASES OF ECONOMIC PLANTS 



In a severe outbreak which is necessary to attract atten- 
tion to the disease the leaves first become covered with 
small dark brown spots, change to yellow, and soon fall. 
By the time the fruit has ripened practically all of the 




Fig. 66. — Anthracnose of white currants. After Clinton. 



leaves may be lost. Upon the leaf stalks, also upon the fruit, 
stems, and canes, the disease appears as little black sunken 
spots. On the berries the spots are circular and black, much 
resembling fly specks. The causal fungus probably winters 
upon the canes, ready to initiate the spring infection. 

Anthracnose can readily be distinguished from the two 
leaf spots mentioned above by the fact that the spots 



SMALL FRUITS 155 

produced in anthracnose are very much smaller, less 
angular, and lack in every way the distinguishing charac- 
ters of the other leaf spots. 

No conclusive evidence as to the best treatment is at 
hand. The best recommendation is probably that of the 
Geneva Experiment Station: " Spray thoroughly with 
Bordeaux mixture, commencing before the leaves appear. 
Make the second treatment as the leaves are unfolding and 
thereafter at intervals of ten to fourteen days until the 
fruit is two thirds grown. In wet seasons make one or 
two applications after the fruit is gathered. When worms 
appear, add Paris green or green arsenoid to the Bordeaux. " 

Rust (Puccinia Ribis DC). — The rust formed upon the 
fruit and leaves of currants is rare in the United States. 
It may be recognized by the sori characteristic of the rusts. 
Diseased parts should be gathered and burned, and the 
bushes and the ground beneath should be thoroughly 
sprayed with a cleansing spray before the leaves appear. 

European rust (Cronartium Ribicola Fisch de Waldh.). — 
This produces an orange-colored powder upon the lower 
surface of the leaves. The spring stage occurs upon trunks 
and branches of the white pine. The disease has been 
rarely noted in America on plants introduced from Europe, 
where it is quite common. 

Powdery mildew, sphaerothecose. See gooseberry. 

Root rot, dematophorose. See gooseberry. 

DEWBERRY 

Double blossom x (Fusarium Rubi Wint.). — Double blos- 
som occurs on dewberry and, to some extent, on the 

1 Written for the authors by Mel. T. Cook. 



156 DISEASES OF ECONOMIC PLANTS 

high-bush blackberry. It is most abundant on the 
Lucretias, but is also a serious pest on the Rathbone. 
The disease makes its appearance in the spring, just as 




Fig. 67. — The Dewberry double blossom showing witches' broom of the vine. 
After Cook. 

the leaf buds are opening, although it can be detected 
previous to that time by the enlargement of the diseased 
buds. 

Instead of the normal shoots and leaves a witches' broom 
is produced ; the entire bud being involved or only a part, 
according to the attack. When the flower buds open, they 



SMALL FRUITS 157 

show a great variety of deformities: sometimes only 
slightly distorted; sometimes with increased number of 
stamens and petals and with enlarged, thickened petals 
and sepals. Even those flowers which appear most 
nearly perfect have diseased ovaries, and the fruits from 
these brooms are always worthless. 

Double blossom usually appears during the second 
harvest and continues to increase until the plants entirely 
succumb. Numerous late blossoms appear during the 
first season and increase in number from year to year. 

The disease is due to a fungus, and the infection of new 
buds occurs during the blooming and fruiting season. 
For this reason it is impossible to control the disease by 
spraying, but it may be held in check by removing and 
burning the deformed buds as soon as they begin to open, 
and can be easily detected. If this is done early in the 
season before the leaves are large enough to hide the dis- 
eased parts, a man working alone can care for plants at the 
rate of 400 per hour. 

Two other diseases are known to be particularly common 
on the dewberry; namely, the leaf blight and the cane 
blight. Both of these are treated under the blackberry 
and raspberry. 

GOOSEBERRY 

The powdery mildew (Sphcerotheca Mors-uvce (Schwein.) 
Berk. & Curt.). — Sphserothecose may be recognized 
by the characteristic mildewed appearance of the leaves, 
stems, and fruit, all of which appear whitened as 
though dusted with blotches of flour. Close inspec- 
tion shows each blotch to consist of cobwebby threads 



158 DISEASES OF ECONOMIC PLANTS 

densely matted in the central portions of the spot, and 
less dense towards its circumference. Later these blotches 
turn brown, irregularly blend into fewer spots, and form 
large diseased areas. As the spot ages, its threads weave 
together into a thick felt. 

The young leaves and growing parts are robbed of 
nourishment, and thus their growth is checked, resulting 
in serious injury. The berries if subjected to one-sided 
attack become deformed and curved, owing to the retarded 
growth of the diseased side. They often crack open and 
decay. Diseased leaves turn brown. Toward the com- 
pletion of the season's growth small, nearly microscopic, 
black perithecia are produced in the centers of the diseased 
spots. 

The damage caused by this disease is excessive and pre- 
sents the most serious obstacle to the successful culture 
of the gooseberry. It has quite prohibited the cultivation 
of the finer sorts of English gooseberries in America and 
is a grave menace to the culture of gooseberries in Europe. 
Its destructiveness is due not alone to the injury to the 
foliage, bush, and to the fruit yield, but also to lack in 
salability, owing to the unsightliness of the partially dis- 
eased fruits. 

This powdery mildew has been very successfully com- 
bated at the New York Experiment Station at Geneva. 1 
Of a large number of fungicides tried potassium sulphide 
proved to be most efficient, using one ounce to two gallons 
of water and spraying seven times. This cost but three 
tenths of a cent per bush for material, and reduced the 

1 Close, C. P., NY. (Geneva) Agr. Exp. Sta. Bui. 161, November, 1899. 



SMALL FRUITS 



159 



percentage of mildewed fruits from sixty-three on the 
untreated bushes to eighteen on the treated bushes. The 
proper time to spray is indicated in the accompanying 




Fig. 68. — Stages at which spraying should be given for mildew. After Close. 

figure. Treatment should be begun at the condition shown 
in the left-hand figure, and continued at intervals of ten 
days or two weeks until seven applications have been made. 
Spraying begun when the bushes are in the condition 



160 DISEASES OF ECONOMIC PLANTS 

shown in the left figure gives decidedly better results than 
when the spraying is delayed until the condition shown in 
the other two figures. 

Black knot. See currant. 

Anthracnose. See currant. 

Septoriose, leaf spot. See currant. 

Cercosporose, leaf spot. See currant. 

Cluster cup (Puccinia Grossularice (Schum.) Lagerh.). — 
Occasionally reddish swollen or thickened spots are no- 
ticed over the leaves and sometimes upon the fruit. 
Close examination shows each spot to consist of a clus- 
ter of minute cups embedded in the tissue of the leaf, 
whence the name " cluster cup." With a lens each cup is 
seen to consist of a fringed rim extending above the surface 
of the leaf, and to be filled with very small red spores. 

The winter condition is found upon quite different plants; 
namely, various common sedges, upon the leaves of which 
it constitutes a genuine rust. 

The damage from this disease is not serious, and no experi- 
ments on a large scale, in prevention, have been undertaken. 
If it should prove destructive, thorough eradication of the 
sedges in the neighborhood, particularly any that are 
rusted in autumn, would be deemed necessary. 

Root rot (Dematophora sp.). — Root rot upon both 
the gooseberry and currant has been reported from some 
states. 

The plants die slowly. When dead and living canes are 
found in the same hill, the living canes are somewhat 
dwarfed. The disease apparently spreads through the 
soil, and the diseased soil area enlarges year by year. Upon 
roots of diseased plants there are conspicuous white threads, 



SMALL FRUITS 161 

the mycelium of a fungus which has been held responsible 
for the damage to the plant although conclusive proof of its 
causal relation to the disease has not yet been adduced. 

Little can be suggested in the way of treatment. It is, 
however, best to pull up and burn affected plants, and it 
is inadvisable to place susceptible crops upon soil which 
is known to be diseased. 

GRAPE 

Black rot (Guignardia BidweUii (Ell.) V. & R.). — 
This widespread and exceedingly destructive disease has 
been responsible for the abandonment of grape raising in 
many sections of the country. It is found in all sections 
to greater or less extent. In 1906 in Michigan the loss from 
black rot was estimated at 30 to 40 per cent of the crop; 
in Ohio in 1905 at 30 per cent of the crop worth $95,000. 
In many sections the loss is practically total unless measures 
are taken to check its ravages. 

In its most familiar form the disease consists of spotting 
and decay of the fruit. Black or brown spots, one or more 
in number, at first infinitesimal in size, appear upon the 
berry. The spots enlarge with great rapidity, one spot in 
a few days encompassing the whole berry and changing it 
into a black mass. As the rot progresses the skin remains 
intact, and soon the berry begins to shrink and shrivel until 
it is eventually merely a dry, hard, wrinkled, mummified 
fruit. The rapidity with which this change takes place is 
shown in the accompanying figure. Many of the berries so 
mummified fall to the ground, others remain upon the vine. 

Upon the leaves the disease appears considerably earlier 
than upon the fruits. Here it produces tan-colored spots 

M 



162 



DISEASES OF ECONOMIC PLANTS 







about 3-8 mm. in diameter, many or few 
according to the severity of the infection. 
In or near the centers of the older spots 
upon the upper surface of the leaves are 
seen the nearly microscopic pycnidia 
which are often arranged in concentric 
circles. 

On the young shoots the spots are some- 
what more reddish and are often cracked 
longitudinally, but otherwise they are as 
upon the leaves. 
;§ This rot is much worse in warm, humid 

£ weather than in dry times, and a few days 
| of muggy weather may so favor the 
§ growth of the causal fungus as to develop 
% an epidemic, which may in turn be 
| checked by a dry spell. Often the dis- 
< ease appears in distinct waves during the 
season, each wave corresponding to a 
climatic condition favorable to infection 
and usually lagging behind such favor- 
able condition a period of 8 to 14 days, 
the time necessary after infection for the 
disease to become conspicuous enough to 
attract the attention of the vineyard- 
ist. The first infections of each season 
occur upon the stem, leaf, petioles, and 
tendrils. 
While the Scuppernong occasionally shows a few spots 
upon leaf or berry and the blossom is sometimes affected, 
this variety is practically immune. 









SMALL FRUITS 



163 



To prevent the inroads of the black rot thorough, clean 
culture should be practiced. All mummified fruit should 
be burned to avoid infection. Keep sprouts and all other 
growths off the ground. Allow no weeds or grass. Plow 
early so as to cover all remaining 
leaves and berries that bear the 
hibernating fungus. Cover crops 
are beneficial. Use a cleansing 
spray while the vines are still 
dormant to clean the bark, trellis, 
etc. The utility of this first 
spraying may vary with climatic 
conditions and latitude. Use 
protective sprays of 4-3-50 Bor- 
deaux mixture * throughout the 
summer. Five or six applica- 
tions are usually necessary. The 
first should be made when the 
shoots are 20-30 cm. long. The 
others at intervals of ten to four- 
teen days. After the first two 
sprayings the spray must reach 
the clusters to be effective. Spray 
each season. Neglect one season brings large increase in 
the rot the following season. 

The following table shows the benefits of careful, thorough 
spraying. 2 




Fig. 70. — Grape black rot. 
Original. 



1 Shear, C. L„ Miles, G. F., and Hawkins, L. A., U.S. Dept. Agr. 
Bur. Plant Indus. Bui. 155. 

2 Wilson, C. S., and Reddick, D., N.Y. (Cornell) Agr. Exp". Sta. Bui. 
266, p. 405. 



164 DISEASES OF ECONOMIC PLANTS 

Result of Bla.ck Rot Experiments in 1908 



Plat 
No. 


Treatment 


Net 
Weight 
Har- 
vested 


Weight 
Firsts 


Weight 
Wine 


Weight 
Rotten 


Firsts 
Per 

Cent 


Wine 
Per 

Cent 


Rotten 
Per 
Cent 


1 


Bordeaux 
4-4-50, 6 


lb. 


lb'. 


lb. 


lb. 










applications 


8084 


7252 


742 


90 


89.7 


9.2 


1.1 


2 


Bordeaux 
5-5-50, 4 


















applications 


7872 


7461 


305 


106 


94.8 


3.9 


1.3 


3 


Bordeaux 
5-5-50, 6 


















applications 


9157 


8726 


306 


125 


95.3 


3.3 


1.4 


4 


Sprayed ac- 
cording to 
weather con- 


















ditions . . 


7997 


7588 


338 


71 


94.9 


4.2 


0.9 


5 


Cultivated but 


















not sprayed 


3175 


2232 


451 


492 


70.3 


14.2 


15.5 


6 


Neither culti- 
vated nor 


















sprayed . . 


3334 


2169 


594 


571 


65.1 


17.8 


17.1 



Powdery mildew, uncinulose ( Uncinula necator (Schw.) 
Burr.). — This mildew, a native of the United States, first 
noted in Europe about 1845, near London, and shortly after 
in Belgium and France, is said to have reached every grape- 
growing country of Europe before 1851. It increased in 
severity until 1854 when it began to be held in check by 
sulphur applications. It is known in all parts of the United 
States. 

The powdery mildew attacks all parts of the plant except 
the roots, showing first upon both the upper and lower 
surface of young leaves as whitish circular spots, which ap- 
pear somewhat as though dusted with flour. These spots 
enlarge, coalesce, and may cover the whole leaf. The af- 
fected leaf is retarded in growth and becomes distorted. 
Mildewed blossoms fail to set their fruit, and fruit that 



SMALL FRUITS 165 

is mildewed soon ceases growth and falls, or develops ir- 
regularly and fails to ripen. 

The mildew fungus is strictty superficial and may be 
easily rubbed off, leaving a discolored spot. In late stages 
perithecia may be recognized as very small black bodies, about 
0.1-0.12 mm. in diameter, lying within the diseased areas. 
The disease develops in most destructive form in shaded, 
damp, poorly ventilated situations. Rain and fogs favor 
it, while very dry weather inhibits it. The American vines 
are less susceptible than the European varieties. 

Ventilation and removal of shading trees are beneficial. 
Close planting should be avoided in order to allow quick 
drying, and trellises should run in such direction as to allow 
free access of sun. But these means are only palliative. 

To control the mildew in dry climates employ flowers of 
sulphur. The sulphur, when the temperature is above 75° 
F., passes into the air, and its fumes, coming in contact with 
the fungus, kill it. Below the temperature at which sulphur 
is effective the fungus will make but little progress. When 
the air, shade temperature, is from 90° to 95° F., the killing 
effect of the sulphur may be seen within 24 hours 1 ; if above 
100°, one or two days are sufficient to rid the vineyard of the 
disease. The sulphur must be distributed to every part of 
the vine. Sulphur upon the ground is of no use. The vines 
should be sulphured from one to seven times, according to 
conditions, susceptibility, climate, etc. The first sulphur- 
ing should be done when the blossoms begin to open; a 
second application should be made before the first sign of 
the mildew, and other applications should follow as need in- 
dicates. It is necessary to resulphur if from one to two days 

1 Bioletti, F. T., Cal. Agr. Exp. Sta. Bui. 186, February, 1907. 



166 DISEASES OF ECONOMIC PLANTS 

at 90° to 95° or four to five days 85° to 90° do not in- 
tervene before the sulphur is removed by rain. If the 
disease was bad the previous year, it is well to sulphur 
even earlier than indicated above, i.e., when the shoots 
are about 15-20 cm. long. 

After the grapes commence to ripen they are nearly safe 
from mildew, but for the future good of the vine the leaves 
should be protected by further sulphuring if need be. 
Young vines should similarly be protected. To properly 
sulphur use good dust sprayers which give an even flow 
of sulphur and are easy of operation. The cost of sulphur- 
ing an acre three times is about $1.25. 

In climates where sulphur cannot be used to advantage 
reliance must be placed upon Bordeaux mixture applied as 
for the black rot. 

Downy mildew, brown rot, gray rot (Plasmopara viticola 
(Berk. & Curt.) Berl. & De Toni). — Each of the downy 
mildews produces a more or less distinctly visible downy 
or velvety growth upon the affected surface. This ap- 
pearance is caused by myriads of spore-bearing stalks 
that rise from the diseased surface. If these stalks. are 
close together, the appearance is thoroughly character- 
istic and the diagnosis clear. As the spores mature the 
spots assume a gray or frosted appearance. 

The European are more susceptible to this mildew than 
the American varieties. All the green parts of the plant 
are affected. Upon the lower. side of the leaf the disease 
may be recognized by the description given above. The 
upper surface of the leaf over a diseased spot becomes 
pale, yellowish, and finally turns brown and dies. The 
area so affected is definitely bordered and does not nee- 




Fig. 71. — Downy mildew as seen from the lower surface of the leaf. After Heald. 



168 



DISEASES OF ECONOMIC PLANTS 



essarily cause the death of the whole leaf, though it may 
do so. 

Upon shoots the same characteristic appearance is noted 
as upon the lower surfaces of the leaves. Sometimes the 




Fig. 72. — Young Niagara clusters attacked by brown or gray rot. After Lodeman. 



death of the affected twig or even of the whole vine results. 
Immature berries which are affected stop growing and de- 
velop the same coating noted upon the leaves, giving rise to 
the name " gray rot." If the berries be more mature when 



SMALL FRUITS 169 

attacked, they turn brown, thus calling forth the name 
" brown rot." The berry in dying shrivels and becomes 
wrinkled, but does not become hard and dry, as in the case 
of the black rot. The disease is usually more troublesome 
in the early part of the season than in autumn. 




Fig. 73. — Bird's eye on the fruit. After Paddock. 

Effective management requires early spraying, though 
sometimes it may be found advantageous also to protect 
the leaves after harvest for the future good of the vine. 
Bordeaux mixture or ammoniacal copper carbonate are the 
most suitable fungicides. 



170 DISEASES OF ECONOMIC PLANTS 

Bird's eye, an thracnose (Sphaceloma ampelinwn DeBy.). 
— This anthracnose, probably introduced into America from 
Europe prior to 1880, is now widely distributed throughout 
grape-growing sections. While not usually so destructive 
as the black rot or the brown rot, it sometimes increases to 
such an extent as to do great damage, even causing in some 
instances the loss of all the berries upon a vine as well as 
much injury to the canes. During damp, warm weather it 
develops rapidly, affecting some varieties more than others. 
The Brighton and Moore's Diamond may be mentioned as 
especially susceptible. 

Upon the canes the anthracnose is first seen as small, dark 
brown or black spots, which soon become sunken in the 
centers. The spots usually enlarge most rapidly in the 
direction lengthwise of the stem, though they may sometimes 
girdle it. Girdling is particularly common upon stem 
clusters, where it is always fatal. The centers of the older 
spots are ashen in color, the edges dark, and the cankerlike 
spot extends from the bark deep into the wood, rendering 
the shoot weak and brittle. 

Upon the fruit spots 3-5 mm. in diameter are produced 
similar to those upon the canes, except that the center does 
not always become ashen. Here, too, a band of red often 
surrounds the diseased part. The parts of the berry adja- 
cent to the diseased spot remain green and develop normally, 
which, associated with the red border, results in the peculiar 
appearance which has led this disease to bear the name 
" bird's-eye disease." 

If the berry is attacked while young, it may either 
outgrow the disease or succumb to it. Several spots 
upon one berry destroy its value, and spots upon one 



SMALL FRUITS 



171 



side may cause distortion, cracking, and exposure of the 
seeds. 

Upon the leaves the dead spots are usually bordered by a 
fine black line, and as the leaf grows the dead tissue of the 
spot may rupture irregularly. 

Badly anthracnosed canes must be cut out and burned, and 
cleansing sprays should be 
used. 

Necrosis (Fusicoccum 
viticolum Reddick) . — This 
disease is said by Reddick 1 
to cause perhaps 50 per 
cent of the death of vines 
usually attributed to root 
worm or other causes. It 
has been noted in New 
York, Ohio, Georgia, Indi- 
ana, and is in some in- 
stances very abundant, 
causing death to 30 per 

cent or more of the vines in the vineyard. The Concord, 
Niagara, Moore's Early, Agawams, Pocklingtons, Wor- 
dens, Lindleys, Catawbas, Isabellas, and Scuppernong are 
affected. 

Necrosis may be recognized in the field by the following 
characters 2 : A trimmed and tied vine that has failed to 
put out shoots; one that has sent forth shoots, the latter 
dying after a few weeks ; vines on which all or part of the 

1 Reddick, Donald, NY. (Cornell) Agr. Exp. Sta. Bui. 263, February, 
1909. 

2 Quoted from Reddick in abbreviated form. 




Fig. 74. 



Necrosis of the vine. After 
Reddick. 



172 



DISEASES OF ECONOMIC PLANTS 



Fig. 75. — Grape ne- 
crosis as it appears 
on the canes. Af- 
ter Reddick. 



shoots and leaves exhibit a dwarfing, with 
leaves small and often crimped about the 
margin ; leaves of nearly normal size but^ 
blanched ; apparently healthy vines with 
leaves and fruit shriveling and dying in 
the summer; fleshy or corky longitudinal 
excrescences on the stem, which in the 
autumn dry down and become reddish 
brown and the following spring slough 
off ; the presence of minute black pustules 
on a dead spur, bark, or wood under the 
bark ; small reddish brown spots 3-4 mm. 
long on the green shoots. 

The disease is conveyed to new tissue 
by spores from the pycnidia, also probably 
by pruning tools which cut sound wood 
after cutting into diseased tissue. It may 
also enter the older parts through wounds. 
Cuttings bearing the fungus probably 
spread the disease. 

Spraying shoots when from 7-J-15 cm. 
long will probably reduce infection. Dis- 
eased vines should be pulled and burned, 
or if the root crown be still sound, they 
may be cut back to near the ground, 
and the renewal will be healthy. In the 
spring and summer it is well to mark sick 
vines for future eradication. Cut off the 
diseased parts, using tools separate from 
those used in ordinary pruning. 

Root rot, dematophorose (Dematophora 
necatrix Hartig). — This rot attacks a 



SMALL FRUITS 173 

few roots at first, but eventually reaches all, and results 
in death of the vine. It is very destructive in Europe 
and has been noted in several places in the United 
States. 

The top growths of affected vines show symptoms first; l 
then follows one division after another until a large vine 
is reduced " to the size of a bushel basket," though numer- 
ous lateral canes may arise, especially near the base of the 
plant. The leaf color usually remains normal with no 
dead tissue, though the leaves sometimes turn yellow, and 
many of then are reduced in size. After the vine dies the 
leaves still remain attached to the canes. 

The mycelium of the causal fungus may be seen as a tufted 
expanse of white dense hyphse, extending along and winding 
about the roots. Later brown hyphse appear. 

The best treatment is to remove and burn the affected 
stock, thoroughly stir, air, and dry the adjacent soil. 

Cercosporose (Cercospora viticola (Ces.) Sacc). — Ir- 
regular dark to black spots upon the leaf often indicate 
this disease. 

The treatment employed for Plasmoporose will be useful. 

Root rot, armillariose (Armillaria mellea Vahl). — Grow- 
ing within the wood of the roots is the root-rot fungus. 
When it has attained sufficient vigor and consumed 
nutriment enough, it develops its spore-bearing part, an 
edible mushroom, from the surface of the diseased wood. 

This mushroom is from 7-12 cm. high with a cap 10-15 
cm. in diameter. The stem is swollen near the base, and 
the cap is conical, fraj^ed at the edge, yellowish, and 
darkened with age. Upon its lower surface are the 

1 Pierce, N. B., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 2, 1892. 



174 DISEASES OF ECONOMIC PLANTS 

gills, white, spotted with reddish brown. It often grows in 
large clusters near the base of the vine. 

The disease occurs in local areas in the vineyard, and the. 
regions of affected soil enlarge irregularly. The disease may 
further be recognized by the fact that the yield is not les- 
sened the first year of the attack; the vine does not succumb 
until two or three years later. The leaves are reduced in 
size, but are normal in color. Upon the roots are found 
dark-colored rootlike cords of mycelium passing into and 
among the irregularities of the bark. 

Excision and destruction of the diseased parts by fire 
will lessen the spread of the disease. 

Bitter rot, ripe rot (Glomerella rufomaculans (Berk.) 
Spaul. & von Schrenk). — Ripe berries only are attacked. 
At the point of injury the color changes to reddish brown 
and eventually the whole berry assumes this color. It 
then decays and finally dries and shrivels. Acervuli appear 
early upon the sunken portion, much as in the black rot, 
except that the berry does not assume the dark hue char- 
acteristic of the latter disease. 

Ammoniacal copper carbonate is recommended as a spray 
as soon as the disease is noticed. 

Bitter rot, melanconiose (Melanconium fuligineum (Scrib. 
& Viala.) Cav.). — The chief effect upon the berry 
as it ripens consists in the appearance of a ripe rot, also 
accompanied by a very bitter taste. The fungus also 
attacks the shoots and stem clusters. 

White rot (Coniothyrium diplodiella (Speg.) Sacc). — 
This disease, known in America since 1887, resembles the 
black rot except as to color. It appears upon the fruit and 
shoots, but is not often serious. 



SMALL FRUITS 175 

Septosporiose (Septosporium heterosporium'Ell. & Gall.). — 
As seen from above in its first appearance upon the leaves, 
this disease resembles the downy mildew. From below the 
spots are round, black, and irregular. As they enlarge they 
may involve the whole leaf. 

This disease is common upon wild vines, often causing loss 
of the leaves in damp situations, but has been as yet of no 
serious injury to cultivated vines in America. 

Scab (Cladosporium viticolum Ces.). — The leaf spots 
produced by this disease show considerable resemblance 
to those of the black rot, but bear no pycnidia. When 
numerous, they coalesce, forming patches of dead tissue. 
They are often bordered by a ring, red in the living 
tissue, black on the dead dried leaf. Spore-bearing hyphse 
abound in the centers of the spots upon the lower side of 
the leaf. 

Pestalozziose (Pestalozzia uvicola Speg.). — This is char- 
acterized by small black pustules under and protruding 
through the epidermis of the fruit and associated with 
rotting. 

It has seldom been observed in America and is as yet of 
small importance. 

RASPBERRY 

Anthracnose (Gloeosporium Venetum Speg.). — The first 
publication in America regarding this disease seems to have 
been made in 1882 by Burrill. 1 

Since then numerous papers from many sections attest 
its importance. It is widely distributed and often serious. 
In 1907 it was estimated to have injured one third of the 

1 Burrill, T. J., Agricultural Review, November, 1882. 



176 DISEASES OF ECONOMIC PLANTS 

crop in Nebraska, 50 per cent in Wisconsin, and even more 
in Illinois. The chief seat of attack is the cane, especially 
young ones, though the disease appears also upon both 
petioles and leaves. 

The fungus often appears upon young canes before they 
are 25 cm. high, making small, purplish spots, which 
soon become grayish or dirty white in the centers. The 
borders of the spots are purplish and slightly raised. 
Later as the spots enlarge they coalesce, making irregular 
blotches 2 cm. or more long, which often encircle the 
cane. The cane then withers and dies from lack of sap 
supply. Badly diseased canes present a bark of rough, 
scabby appearance due to the efforts of the cane to heal 
the wound. Canes occasionally crack from this disease. 
The chief injury is to the cambium layer or the sappy 
outer wood. The leaves on affected canes are dwarfed, 
the fruit ripens prematurely, is undersized, and often 
dries up. 

Upon the petioles of the older leaves the disease 
appears early, spreading thence along the ribs to the leaf. 
Owing to the one-sided attack upon the veins and petioles, 
the leaves develop unequally, often with inrolled edges. 
Upon the lower surface very small spots about 1 mm. in 
diameter are produced, from which the diseased tissue 
often falls. In the older diseased spots the spore-bearing 
acervuli are just visible to the naked eye. 

Occasionally the disease, even though bad, may escape 
observation during the first and second years, and even 
well into the third year. Then, with prospect of a good 
yield, the berries may shrivel on the stems and later many 
plants may die. More often the disease remains moder- 



SMALL FRUITS 177 

ately injurious from year to year, weakening the plants and 
diminishing the yield. 

In localities subject to this disease it is best to rotate 
crops so as to avoid keeping raspberries more than three 
years on the same soil. When the disease appears, cut out 
and burn diseased parts immediately after picking. Spray- 
ing young canes with a protective (Bordeaux) spray the 
following spring will lessen infection. Whether the spray- 
ing is of enough benefit to warrant its use is questionable. 1 
If spraying is done, it should be begun when the new canes 
are about 15 cm. high, and one or two more sprayings 
given at intervals of 10 or 14 days thereafter. 

Crown gall (Pseudomonas tumefaciens Smith & Town- 
send). — Frequently small swellings are noticed on the 
roots of the raspberry in abundance enough to injure the 
health of the plant. These galls very closely resemble 
the crown gall of the peach, almond, apple, etc., which has 
recently been attributed to a species of Pseudomonas. It 
is desirable to pull up and destroy diseased plants and avoid 
placing blackberries and raspberries on ground which is 
known to be affected. 

Leaf spot, septoriose. See blackberry. 

Rust, gymnoconiose. See blackberry. 

Cane blight (Coniothyrium Fuckelii Sacc). — First 
noticed in literature in 1899 by Stewart and Eustace 2 as 
occurring in the Hudson valley, this disease seems to be 
widespread and destructive upon both red and black rasp- 

1 Paddock, W., N.Y. (Geneva) Agr. Exp. Sta. Bui. 124, p. 273, April, 
1897. 

2 Stewart, F. C, and Eustace, H. J., N.Y. (Geneva) Agr. Exp. Sta. 
Bui. 226, December, 1902. 

N 



178 DISEASES OF ECONOMIC PLANTS 

berries. Principal damage occurs to the fruiting canes, 
the foliage of which suddenly wilts and dries. New canes 
are frequently killed during the first season's growth. 
The disease often starts in stubs exposed in pruning, and 
progresses toward the root. 

Infection usually occurs through wounds, especially 
pruning wounds, or those made by insects. Sometimes 
the disease remains upon one side, while in other cases it 
encircles the cane. 

Upon diseased canes the bark is lighter colored and 
disfigured by smoke-colored patches of spores extruded 
from the pycnidia within. The pycnidia appear as very 
minute pustules. The wood is much discolored and even- 
tually brittle. This cane blight is often attributed to a borer 
or to drought or winter injury. 

The damage is often as high as 25 or 50 per cent of 
the crop, and the disease is said to be present to some 
extent in nearly all the raspberry plantations in New 
York. Cuthbert, Marlboro, Ohio, Gregg, Kansas, and 
the wild red raspberry are susceptible. Columbiana is 
more resistant. 

The disease is disseminated largely by diseased nursery 
stock or even in the dirt upon the roots of plants from 
diseased fields, and is conveyed from plant to plant by 
wind or rain, by pickers, and by workmen while pruning 
and layering, also by tools in cultivation. See soil dis- 
eases. Since the fungus can live on dead fragments of 
canes, etc., upon the ground, these prove fruitful means 
of propagating the pest. 

To prevent the disease care in the selection of healthy 
plants and planting area is necessary. Plants should not 




FlG# 76. — Raspberry cane blight. After Stewart and Eustace. 



180 



DISEASES OF ECONOMIC PLANTS 




Fig. 77. — Raspberry dis- 
colored by Sphserellose. 
After Stewart and Eus- 
tace. 



be set where the disease has been in 
previous years. When the fungus 
has gained access to a plantation, all 
dead canes should immediately be 
cut out and burned and all frag- 
ments scrupulously removed from 
the ground. Spraying is of doubtful 
value. 

Sphaerellose (Sphcerella rubina 
Stewart and Eustace). — On red 
raspberry canes in autumn sharply 
denned brown or bluish black areas 
from 2-10 cm. long occur on the 
bark, never on the wood. In the 
spring these spots bear numerous 
small pycnidia. 

This disease, due to Sphserella, does 
not often cause appreciable injury. 

Yellows. — Plants in this disease 
are stunted, yellowish, and recall 
peach yellows. 1 Laterals are dwarfed, 
leaves are small, curled downward at 
the margins, and yellow mottled. 
Berries dry up without ripening or 
are insipid when mature. Health 
and disease may occur upon the 
same plant. The cane itself and 
roots appear normal. 



The cause and remedy are not yet known. 



1 Stewart, F. C, and Eustace, H. J., N. 
Bui. 226. 



(Geneva) Agr. Exp. Sta. 



SMALL FRUITS 



181 



STRAWBERRY 



Leaf spot (Sphcerella fragarice (Tul.) Sacc). — The most 
conspicuous disease of the strawberry, one nearly al- 
ways present to some extent on both wild and culti- 




Fig. 78. — Strawberry leaf spot. After Freeman. 

vated varieties, is known by the presence of small 
4-6 mm. purple or red bordered spots upon the leaves, 
the older spots bearing white or ashen centers. Late in 
the development of the spots the hyphse of the causal 
fungus are barely visible in these centers with a good hand 
lens. The spots, when dimerous, may coalesce, forming 



182 DISEASES OF ECONOMIC PLANTS 



■ 



large, irregular blotches. The disease is also very injuri- 
ous in its attacks upon the fruit stems, resulting in 
diminution of food supply to the fruit and its improper 
development. 

It attacks all varieties, precluding the use of especially 
susceptible varieties in some localities, often killing 
the plants, and in any event lessening their vigor and 
productiveness. In some localities entire plantings have 
been destroyed. One grower reports a loss of $1500 on 
a six-acre field in one season. 

Moisture and heat favor the disease, while moisture, 
dew, etc., upon the leaves are necessary to infection. 
Weather favorable to infection followed by hot, dry days 
may be attended by great injury. Plants growing upon 
heavy, wet, undrained soil suffer more than those upon 
dryer soil. 

The following comparison of resistance is quoted 1 : — 

" 1. Blight very rare — Daisy, Eureka, Jewell, Tri- 
umph de grande. 

" 2. Blight rare — Belmont, Lady Rusk, Scarlet Queen. 

" 3. Blight frequent — Annie Forest, Bomba, Bubach, 
Burt, Captain Jack, Covill, Crawford, Cumberland Tri- 
umph, Dutter, Gandy, Gold, Gypsy, Haverland, Hender- 
son, Itaska, Jessie, Lida, Logan, Mammoth, May King, 
Miami, Ontario, Parry, Pearl, Phelps, Pineapple, Primo, 
Summit, Sunset. 

" 4. Blight abundant — Barton's Eclipse, Cloud, Gandy 
Pride, Great America, Loudon's 15, Piper. 

"5. Blight very abundant — Monmouth, Ohio, Photo, 
Sanafee, Warfield." 

1 Garman,' H., Ky. Agr. Exp. Sta. Bui. 31, p. 13. 



SMALL FRUITS 183 

Hume reports the Lady Thompson and Michel's Early 
as quite resistant. 

Frequent change of beds; also cutting, gathering, and 
burning or burying of tops in place after harvest lessens 
this disease. The use of Bordeaux after the removal of 
the diseased leaves will also lessen the infection of the 
next year. 

. Hume * in Florida found that three early sprayings of 
4-4-40 Bordeaux mixture checked the disease completely, 
so that " it was a difficult matter to find a leaf at all dis- 
eased in the whole patch." Later, when the disease began 
to make headway again, another spraying stopped it. 

Leaf blight, aposphaeriose (Aposphceria sp.). — This dis- 
ease was first found by Stevens 2 in 1892 in New York and 
in New Jersey, 2 and it is probably of wide distribution. 
It is in some instances very destructive, causing loss of more 
than half the crop. It may be distinguished from the other 
leaf diseases by the shape of its spot, which usually begins 
at the leaf margin and extends toward the center, forming 
a more or less V-shaped region. The spots are brown. 

The treatment should be the same as that for Sphserellose. 

Leaf spot, ascochytose (Ascochyta fragarice Sacc). — This 
leaf spot is very similar to sphaerellose, for which it may be 
mistaken without microscopic diagnosis. The treatment 
for the two is the same. 

Powdery mildew, sphserothecose (Sphcerotheca humuli 
(DC.) Burr.). — This mildew may be recognized by the 
characters usually pertaining to the powdery mildews. 
(See grape.) 

1 Hume, N. EL, Fla. Agr. Exp. Sta. Rpt. 1901, p. 95. 

2 Halsted, B. D., N, J. Agr. Exp. Sta. Rpt. 1893, p. 329. 



184 DISEASES OF ECONOMIC PLANTS 

Upon the strawberry it induces curled, inrolled leaves 
and the white mycelium is found upon their lower surfaces. 
The disease is not usually very troublesome. 



TROPICAL FRUITS 
AVOCADO 

Anthracnose (Colletotrichum glcesporioides Penz.). — 
Attack upon the leaves eventually causes defoliation. 
Early infection of the fruit results in its complete loss. If 
the fruit is not attacked until late, it may remain upon the 
tree, but becomes spotted with brown and finally cracked. 
On both leaves and fruit it can be controlled by the use of 
Bordeaux mixture. 

CITRUS FRUITS 

Brown rot (Pythiacystis citrophthora Sm. & Sm.). — 
This fungous disease has caused a very considerable loss, 
30 per cent in some cases, in California for the past seven 
or eight years, 1 but the real cause of the trouble was not 
known until 1906 or 1907. It chiefly affects the fruit after 
it has been packed and shipped to market, although the 
infection takes place in the orchard or packing-house 
where the disease is largely disseminated by the fruit 
washers. 

The rot has a peculiar characteristic rancid penetrating 
odor, and its presence is further indicated by an abundance 
of small flies in boxes where there is any diseased fruit. 
One affected fruit in a box communicates disease to the 
whole. 

1 Smith, R. El, Cal. Agr. Exp. Sta. Bui. 190, July, 1907. 



TROPICAL FRUITS 185 

The brown rot is found in its purest condition on the 
fruit in the orchard, especially the fruit on the ground or 
hanging low on the tree. It is most prevalent in wet 
weather or on low ground after irrigation. The fungus is 




Fig. 79. — Brown rot of lemons, showing white growth of the fungus. After R. E. 

Smith. 

visible to the eye in the packing-house, as of a mass of 
white filaments. It is spread by contact alone. 

Orchard infection can be controlled by the use of a 
heavy mulch under the trees, either straw or a heavy cover 
crop. In the packing-house the use of disinfectants in 
the washer prevents trouble; one and one half pints of 
formalin in the morning, and 1 pint at noon, or 1 pound of 
bluestone in the morning and 8 ounces at noon. 

Scaly bark. — Small, circular or oval, rusty-colored bark 



186 DISEASES OF ECONOMIC PLANTS 

spots, with well-defined margins, characterize this disease. 
The bark cracks and forms scales. The spots are at first 
scattered, but in time coalesce and form large areas upon the 
larger branches and trunk, giving it a scaly appearance. 

Sweet oranges are most affected, the fruit ripening 
prematurely. It is claimed by Fawcett l that the disease 
may be due to the wither-tip fungus. 

' Top working is recommended, also heading back and 
painting the trunk and the stumps of the branches with 
carbolineum, one part to one part of water. 

Gum disease. — Several diseases recognized by the exuda- 
tion of gum from the trunks and branches of the trees are 
called " gum diseases." Their causes are not definitely 
known; by some they are attributed to mechanical injury 
alone ; by others to poor cultivation or water injury in ir- 
rigation ; by others to the presence of soil around the trunk. 

Sooty mold (Meliola Camelliae (Catt.) Sacc). — Sooty 
mold has been known in Florida for twenty or twenty- 
five years, but was at first considered to be of but little 
import, though it is now regarded as injurious to both fruit 
and trees. The disease covers the fruit and leaves with 
a black, velvety, membranous coating which may be stripped 
from the leaves. 

As the disease follows certain insects that exude a honey- 
dew, it may be successfully combated by destroying these 
insects. Fumigation or thorough spraying with a resin 
wash or kerosene emulsion is recommended. 

Blue mold (Penicillium italicum (Wehm.), and Penicillium 
digitatum (Fr.) Sacc). — This decay of citrus fruits in transit 
from California causes a loss estimated at from $500,000 

1 Fawcett, H. S., Fla. Agr. Sta. Bui. 98, Mch. 1909. 



TROPICAL FRUITS 187 

to $1,250,000 annually. Careful investigations of G. H. 
Powell and his assistants have shown that the chief 
trouble results from handling the fruit in such way as to 
wound it, and thus provide an entering point for the fungus. 
Without mechanical injury no decay from blue mold can 
occur. Hence the only method of control that is necessary 




Fig. 80. — Two forms of blue mold : at left, Penicillium Italicum ; at right, P. digita- 
tum. After R. E. Smith. 

is painstaking care in handling the fruit to prevent bruising 
or puncturing the skin. 

Black rot (Alternaria Citri Pierce). — This disease was 
described and its cause given by Pierce in 1902. It attacks 
only the navel orange, causing from 2 to 5 per cent loss 
of the whole crop. It is easily recognized by the prema- 
ture ripening which it induces, and by the deep red color 
and extra large size of the fruit. The diseased fruits are 
very conspicuous on the trees before the main crop has 
colored. 

The spores of the fungus that causes the decay gain en- 



188 



DISEASES OF ECONOMIC PLANTS 



trance through slight imperfections of the skin at the navel 
end and make rotten areas under the skin. 

All diseased fruit should be collected and burned or 
buried deeply. 

Scab (Cladosporium elegans Penz.). — The scab has been 




Fig. 81. — Scab of the sour orange. After Hume. 



known for twenty years, and occurs on the sour citrus fruits 
such as the pomelo, kumquat, and sour orange, though its 
presence on the last is of little importance. 

The disease attacks the young leaves, twigs, and fruit, 
and causes them to produce conspicuous, warty, corky 



TROPICAL FRUITS 



189 



growths, that give a rough, uninviting appearance. Often 
the leaves are twisted and drawn out of shape. The warts 
are at first yellowish, but as the disease ages they become 
almost black, and finally crack open. 

Ammoniacal copper carbonate or Bordeaux mixture will 
prevent this. 

Anthracnose, wither 
tip (Colletotrichum gloeos- 
porioides Penz.). — In 
this disease the leaves 
become spotted. The 
spots are circular in out- 
line, yellowish in color, 
and bear small, dark 
spots, the filaments and 
spores of the causal 
fungus. 

The disease also oc- 
curs upon the fruit of 
various citrus trees. 
Rolfs noted its attack 
upon the lemon, where it caused the fruit to fall pre- 
maturely, and Hume reports that it may occur upon the 
pomelo either before or after the fruit is picked. Here the 
disease causes brownish spots which enlarge with age and 
become dirty black in color. The fungus invades the in- 
terior of the fruit as well as the rind. 

In all possible cases the diseased parts should be cut out, 
care being taken to cut far enough back to get all injured 
parts; also affected fruits should be removed and destroyed. 
Spraying with Bordeaux mixture controls the disease upon 
the fruit. 




Fig. 82. — Orange leaves showing spots caused 
by anthracnose. After Hume. 



190 



DISEASES OF ECONOMIC PLANTS 



Foot rot, mal-di-gomma (Fusarium Limonis Briosi). — 
The first symptoms of the disease are abundant exuda- 
tions of gum upon the trunk of the tree ; at the same time 
the bark becomes brownish in patches, which are thrown 
off and other patches come. The tree appears as though it 
does not secure sufficient nourishment, the leaves becoming 
yellow, scanty, and smaller than usual. 

Though the trees bear considerable fruit, the amount 
of damage in Florida is estimated at $100,000 annually. 
No treatment has proved satisfactory. 



FIG 

Fruit rot (Colletotrichum Carica S. & H.). — This disease 

was first described in 1909 by the authors. A rot due 

to an undescribed species of 
Collectotrichum, and possibly 
identical with this, was re- 
ported from Louisiana in 
1907. 

Fruit rot is easily recog- 
nized by the sunken, rotten, 
more or less circular fruit 
spots, nearly always covered 
with a white mass of fungous 
mycelium. As they grow 
older they produce numerous 

pustules of the salmon-pink color characteristic of the 

spores. 

The amount of damage caused is very great by reason 

of premature falling of the fruit, at times destroying the 

whole of the crop. 




Fig. 83. — Fig in well-advanced stage 
of fruit rot. Original. 



TROPICAL FRUITS 191 

Infected fruit should be gathered and destroyed and 
the bushes should be given a dormant spray and two or 
more applications of Bordeaux mixture when in foliage. 

Rust ( Uredo Fid Cast) . — This rust does considerable 
damage to the fig crop, causing premature falling of leaves 
and thus removing a source of nourishment for the 
development of the fruit. The rust appears as brown 
spots upon the leaf, which can easily be seen with the aid 
of a lens. 

Root rot (Dematophora necatrix Hartig). — Attack upon 
the roots of the fig at any period of growth, a sudden loss 
of leaf, and premature death characterize this disease. 

The one treatment is to remove the diseased bushes and 
thoroughly stir and dry the soil where the disease occurred. 
See grape. 

Leaf blight (Cercospora Bolleana (Thuem.) Speg.). — 
This disease has been noted in the United States, though 
but slight attention has been given it. It causes injury 
similar to that of rust. 

Texas root rot. See cotton. 

Yellow rust (Fusarium roseum Link). — This disease 
attacks the leaves, causing yellowish spots which fall away, 
giving the leaf a ragged appearance. 

GUAVA 

Ripe rot (Glomerella psidii (G. Del.) Sheldon). — This 
disease was described from greenhouse material collected 
at Washington, D.C., and afterward it was reported from 
Florida and California. The affected fruit shows circular 
brown decayed areas. In the older stages of the disease 
masses of salmon-colored spores are visible over the decayed 



192 DISEASES OF ECONOMIC PLANTS 

areas. The entire fruit at length becomes rotten, wrinkled, 
and shrunken. 

LOQUAT 

Scab (Fusicladium dendriticum (Wallr.) FckL, var Eriobo- 
tryce Scalia.). — This disease is reported as very serious 



rcl ^f IP 



Fig. 84. — Guava affected with ripe rot. After Rumsey. 

upon both fruit and leaves in the western part of California. 
Anthracnose, blossom blight. See citrus fruits. 

MANGO 
Anthracnose. See citrus fruits. 

OLIVE 

Knot (Pseudomonas Savastanoi E. F. Smith). — Tu- 
bercles or galls upon the leaves and branches, and even 



TROPICAL FRUITS 



193 



upon the trunk of the tree, are the first signs of attack. 
Upon the leaves, the knots are always small, particularly if 
they are numerous. Upon the small twigs the knots 
attain the size of a garden pea, while upon the trunk they 
become 2-3 cm. or more in diam- 
eter and finally destroy the tree. 
The disease was noticed in Cali- 
fornia in 1893 and appears to be 
confined to a very small range. 

Peacock leaf spot (Cycloconium 
oleaginum Cast). — According to 
Bioletti this disease is very prev- 
alent in certain regions of Cali- 
fornia, occasionally causing the 
leaves to turn yellow and injur- 
ing the appearance of the fruit. 
Usually it does but little harm. 
Spots 2-4 mm. in diameter occur 
upon the leaves. They are com- 
posed of concentric rings of differ- 
ent colors, giving them somewhat 
the appearance of the spots on 
a peacock's tail feathers. The 
spots on the fruit are smaller and 
more decidedly brown in color. 

The use of Bordeaux mixture checks the trouble. 

Sooty mold. See citrus fruits. 




Fig. 85 



194 DISEASES OF ECONOMIC PLANTS 

VEGETABLE AND FIELD CROPS 

ASPARAGUS 

Rust (Puccinia Asparagi DC). — The asparagus rust, 
though observed in Europe as early as 1805,. was not 
noted in epidemic form in the United States until 1896, 
when it was recorded by Halsted 1 as occurring in sev- 
eral New England States. In 1897, though it had extended 
to South Carolina and to some extent westward, the interior 
and western part of the United States seemed still free 
from it. In 1898 it was first found in Michigan; in 
1899 in Illinois, Ohio, and Kansas; in 1900 in Dakota, 
Nebraska, and Texas, completing its westward march into 
California in 1900 or 1901. It is now known in every state 
where asparagus is grown. 

The rust usually first attracts attention by its effect 
upon the green tops which redden under the disease, this 
symptom appearing at any time after blossoming or com- 
ing to leaf. Diseased areas in the field enlarge rapidly, and 
soon the affected leaves yellow and fall, leaving the bare, 
dead stalks. Close examination of the diseased regions 
in the field shows that the twigs and leaves bear many small 
blisters (sori), consisting of the raised skin of the plant. 
Under this skin is a mass of powder nearly the color of iron 
rust. In early stages of attack these blisters are few and 
scattered, but they rapidly increase in number. When 
young, the skin covering the sori is unbroken; later it rup- 
tures, setting loose the rusty powdery mass of spores be- 

1 Halsted, B. D., N.J. Agr. Exp. Sta. Rpt. 1893, p. 329, and N.J. Agr. 
Exp. Sta. Bui. 129, 



VEGETABLE AND FIELD CHOPS 



195 



neath. This, the summer stage, is chiefly responsible for 
the hibernation of rust in the east. Later in the season 
the sori become black 
instead of rusty col- 
ored, thus constituting 
the winter stage of the 
rust. 

In the spring still an- 
other stage, the spring 
stage, may occasionally 
be seen, though it is 
rare east of the Rocky 
Mountains. This con- 
sists of small, oval, pale 
spots upon the branches 
or leaves. In the cen- 
ters of these spots small 
round pustules develop 
in concentric lines. 
Soon each pustule 
opens, constituting a 
very minute cup which 
is sunken into the leaf. 
From these cups issues 
a powder quite similar 
to that from the sori of 

the summer stage, though-more orange in color. All three 
stages of rust — spring, summer, and winter — may occur 
simultaneously upon the same plant. 

The disease spreads rapidly throughout the field during 
the spring and summer stages. The winter stage is the 




Fig. 



, — Sori of the asparagus rust upon the 
stems, enlarged. Original. 



196 DISEASES OF ECONOMIC PLANTS 

hibernating condition in which the causal fungus must rest 
until the following spring before it can induce further in- 
fection. 

During the first two stages spores in enormous quanti- 
ties are liberated by the least movement of the plants 
by animals or wind, and the spores, carried to their 
new prey, produce infection if conditions of moisture are 
present. 

The effect upon the plant is serious. While the salable 
part of the plant is not attacked, the green part is largely 
decreased and its starch-forming power diminished, so that 
the amount of nutriment that can be stored away in the 
underground parts is lessened. This must result in dimin- 
ished vigor and productiveness of such roots the following 
season. 

The loss may range from 15 to 35 per cent of the crop 
the year after the first attack, while in three years the 
more susceptible varieties may be so nearly destroyed that 
the beds must be abandoned. In some states the invasion 
of this disease has almost, if not quite, prohibited com- 
mercial asparagus growing. 

The rust is most injurious in light dry soil ; irrigation is, 
therefore, beneficial. Dew has been found to favor the 
rust ; therefore shaded, dewy localities should be shunned, 
as should also rows running at right angles to the prevailing 
winds. Clean culture methods, cutting and burning all 
tops in the fall, and destroying all wild asparagus aids in 
preventing the propagation of the rust. 

The Palmetto varieties are quite resistant and offer a 
solution of the rust problem in some localities. In dry 
climates dusting with sulphur 150 to 200 pounds per 



I 



VEGETABLE AND FIELD CROPS 



197 



acre about three weeks after cut- 
ting is finished and before the rust 
appears is beneficial. 1 It is best to 
sulphur early, and only when dew 
is present. 

In regions subject to rain, where 
the sulphur treatment is not appli- 
cable, three sprayings with sulphur- 
soda soap are recommended : first 
in July, with other applications at 
intervals of three weeks. In New 
York three sprayings with Bordeaux 
mixture with resin added as an ad- 
hesive gave a gain of $132.75 per 
acre. 2 

Colletotrichose (C 'oil etotri chum 
sp.). — This disease is known by 
its very numerous black acervuli 
borne in a blanched background 
upon the stem. It develops late in 
the season. 

Leopard spot. — The asparagus 
leopard spot is strikingly suggestive 
of its name. It consists of long ir- 
regular spots, ashen in color, . with 
dark borders. No treatment is 
known. 



r 



* 






rW' 



a. 



'<. . 




. 



* Smith, R. E., Cal. Agr. Exp. Sta. Bui. 
165, January, 1905. 

2 Sirrine, F. A., N.Y. (Geneva) Agr. Exp. 
Sta. Bui. 188, p. 251, & Bull. 189. 



Fig. 87. — Anthracnose 
spots upon bean pods. 
After Stewart. 



198 DISEASES OF ECONOMIC PLANTS 

BEAN 

Pod spot, anthracnose (Colletotrichum lindemuthianum 
(Sacc. & Magn.) B. & C.). — First described in 1878 
in Germany, this disease is very widely known and is 
especially destructive. It develops so rapidly that beans 
delivered to the cars for shipment in apparently healthy 
condition may, upon arrival at their destination, be quite 
badly spotted. The loss is often 20 per cent, and occa- 
sionally is reported as total. 

Upon the pods the disease appears as dark-colored spots, 
usually sunken, varying in size from 1-10 mm., or more if sev- 
eral spots coalesce. The border of the spot is often tinged 
with red, the center rust colored. Old pod spots overly- 
ing seeds within cause spots upon these seeds. The pod 
spots are much more noticeable and unsightly upon light- 
colored than upon green beans. 

Upon the stems and leaves similar spots are found. 
They are especially noticeable upon young stems still 
blanched and upon the seed leaves. On older leaves they 
may be upon the veins, blackening and killing them and 
bringing death to the leaf. Leaves are thus often entirely 
cut off from the plant. 

The wax varieties are especially susceptible, while the 
limas are quite resistant. 

The fungus is carried to fields largely by diseased seeds, 
by beans bearing the spots above mentioned. Such seeds 
result in infected seedlings which serve as a multiplying 
ground for the fungus and result in its spread and general 
attack upon the field. 

In fields where the disease is well established upon stems 
and leaves the damage is great in loss of starch-producing 



VEGETABLE AND FIELD CROPS 



199 



power through the destruction of green tissue. Still greater 
loss follows from the spread of the disease to the pods as 




Fig. 88. — Bean anthracnose upon stem and leaves of young plants. After Whetzel. 

they form, the unsightliness of the spotted pods greatly 
injuring their salability. 



200 



DISEASES OF ECONOMIC PLANTS 



Since the spores are spread only when they are wet, 
handling or disturbing the vines in any way while the 




Fig. 89. 



Bean rust upon leaf and pods ; note the numerous sori upon both surfaces. 
After Beach. 



dew or rain is still upon them should be avoided. Seeds 
already bearing the fungus, i.e., spotted seeds, should 
never be planted, since they not only raise sick plants, 



VEGETABLE AND FIELD CHOPS 201 

but also carry the disease to the field to infect other plants. 
One infected seed in a thousand is enough to infect the 
field, and spraying is not effective 1 to check the spread of 
the disease after infection occurs. Since no effective rem- 
edy is at hand except the use of healthy seed, the greatest 
care should be given to this point. Home fall-grown seed 
known to be free from disease is preferable to seed of un- 
known origin that is perhaps diseased. If a few seeds 
known to be free from disease can be secured and multi- 
plied in a special seed plot, they will give clean seed for 
future use. Treatment of the seed to kill the fungus is not 
yet upon a practicable basis. Clean culture, the removal 
from the field and destruction of diseased stalks and plant 
parts eliminates a source of spring infection which may be 
important. 

Rust (Uromyces appendiculatus (Pers.) Link). — This 
rust may be recognized by its sori upon the leaves 
and occasionally upon other structures. The sori are at 
first blisters of pinhead size, covered by the epidermis of 
the plant. Later this covering ruptures and discloses a 
mass of spores the color of iron rust, or later in the season 
chestnut colored, which fall away in quantity, smudging 
the leaf and spreading the disease. The upper side of the 
leaf opposite a sorus usually shows a spot, pallid, yellowish, 
lacking in true leaf-green color. Sori are sometimes found 
upon the upper surface, but not so frequently as upon 
the lower. 

The rust usually develops somewhat late in the season 
and is not so destructive as are many of the other bean 
troubles. 

1 Whetzel, H. H., N.Y. (Cornell) Agr. Exp. Sta. Bui. 255, May, 1908. 



202 DISEASES OF ECONOMIC PLANTS 

It is reported upon many species of true beans (Phaseolus) 
and upon related genera a Visgna, Falcata, Strophostyles. 
If the disease proves destructive, clean culture, the de- 
struction of all wintering forms, is advisable. 

Blight (Pseudomonas phaseoli E. F. Smith). — Beans of 
various kinds are subject to a blight which manifests 




Fig. 90. — Bacteriosis of bean leaves. After Fulton. 

itself upon the pod, leaf, or stem. It has been reported 
from various states, from Canada, is widely distributed, 
and often quite destructive. It was first observed by 
Beach 1 in New York. 

Usually the leaves are the parts first attacked. Here 
large watery patches, brown in color r are produced. 
These spots later dry, become papery in texture, and 
rupture, leaving the foliage ragged and torn. After 

1 Beach, S. A., N.Y. (Geneva) Agr. Exp. Sta. Bui. 48, December, 
1892. 



VEGETABLE AND FIELD CROPS 



203 



the leaves, and from them the pods, soon become in- 
fected with watery, ulcer-like spots without definite bound- 
ary, similar to 
those upon the 
leaves, though 
often amber 
coated. Attack 
upon young pods 
kills them. 

This disease is 
carried over the 
season largely by 
infected seed and 
is conveyed from 
plant to plant in 
the field by in- 
sects. 

Diseased seed 
and seed from 
fields bearing the 
disease should 
be avoided, and 
clean culture, in- 
cluding the burn- 
ing of all infected 
plant parts, 
should be prac- 
ticed. The fol- Fig. 91. — Bacteriosis of the bean. After Halstead. 

lowing list shows 

the variation in resistance, the least susceptible being 

placed first and the most susceptible last: Schindler's 




204 



DISEASES OF ECONOMIC PLANTS 



Round Pod Wax, Refugee Wax, Burpee's White Wax, 
GrenelPs Rust-proof Golden Wax, Wardwell's Kidney Wax, 
Dwarf German Black Wax, Early Valentine. 1 

Stem rot, pod rot (Rhizodonia sp.). — This disease is 
manifest in three forms : 2 — 

1. Damping off of seedlings. See damping off. 

2. Dry rot of the stem. In this condition the tissue is 
dead, discolored, and dry-rotted at from 2-5 cm. above the 




Fig. 92. — Bacterial disease upon bean seeds. After Clinton. 

ground. The rot extends to the pith and usually encircles 
the stem, and thus so weakens the plants that they are 
often broken by the wind. In any event they soon wilt 
and die. 

3. As brown sunken areas upon pods, penetrating to 
and discoloring the seeds. The germination of the seed is 
not stopped by this attack, and a fruitful source of dissemi- 
nation is thus afforded. Such seeds should be avoided. 3 

Downy mildew (Phytophthora Phaseoli Thaxt.). — The 
downy mildew is a northern disease regarded by Halsted 4 



1 Duggar, B. M., and Stewart, F. C, N.Y. (Cornell) Agr. Exp. Sta. 
Bui. 186, January, 1901. 

2 Fulton, H. R,., La. Agr. Exp. Sta. Bui. 101, January, 1908. 

3 Hedgcock, G. G., Sci. n. s. 19, 268, February, 1904. 

4 Halsted, B. D., N.J. Agr. Exp. Sta. Bui. 151. 



VEGETABLE AND FIELD CROPS 205 

as the most serious disease of the lima bean. It was first 
observed by Thaxter in 1889. 1 

Upon the pods the disease appears as dense, woolly-white 
growths in irregular patches. These consist of myriads of 
the spore-bearing hyphae of the causal fungus, laden with 
their spores. 

The mildew also attacks young shoots, petioles, flower 
clusters and leaves, causing them to develop in dwarfed, 
imperfect fashion and destroying their value. 

The spores are largely carried by nectar-seeking insects, 
as is shown by the abundance of flower infection. Spores 
are also carried by wind. Even in a season favorable to 
the development of the disease thorough use of Bordeaux 
mixture, three sprayings, will insure the crop. The de- 
struction of infected trash is advisable. 

Southern blight (Sclerotium Rolf six, Sacc. in litt.). — 
The symptoms are wilting of the leaves, temporary re- 
covery, yellowing, djdng, and eventually dropping. The 
fungus usually attacks the plant just below the surface of 
the ground, invades the cambium, and destroys it. For 
further details see pepper. 

Leaf blotch, cercosporose (Cercospora cruenta Sacc). — ■ 
This occurs only upon the foliage as brownish patches, 
causing the leaves to fall away. The spots are large, 
angular, and limited by the vines. 

Leaf spot, isariopsose (Isariopsis griseola Sacc). — 
This disease is chiefly limited to the foliage, producing 
small, angular spots, over the under surf ace of which the 
fungus forms a gray, moldy covering. 

Pod blight (Phoma subcircinata Ell. & Ev.). — Phomose 

1 Thaxter, R., Bot. Gaz. 14, 273, November, 1889. 



206 



DISEASES OF ECONOMIC PLANTS 




is destructive upon the lima bean, producing upon pods 
and leaves large, brown patches, with the pycnidia ar^ 
ranged in concentric circles. When the disease is very 

prevalent, the pods fail to 
mature their seeds. 

Spraying with Bordeaux 
mixture is recommended. 

Powdery mildew (Ery- 
siphe polygoni DC). — The 
characters of the powdery 
mildews as described for 
the grape apply here suffi- 
ciently to serve for recog- 
nition purposes. This dis- 
ease is not usually serious, 
and is amenable to treat- 
, ment with flowers of sul- 
phur or spraying with liver 
of sulphur. 

BEET 





Fig. 93. — Lima bean pods showing Pho- 
mose. After Halsted. 



Leaf spot (Cercospora 
beticola Sacc). — This, one 
of the several leaf spots 
upon the beet, is very widespread in the eastern and middle 
states. Very few fields are entirely free from it. It occurs 
upon all varieties, but is especially injurious to the sugar 
beet. 

The round, brownish, purple-bordered spots turn ashen 
in the center, and when mature, often become so thin and 
brittle as to drop out, leaving ragged holes. The sporif- 






VEGETABLE AND FIELD CHOPS 207 

erous hyphse may be seen with a good lens upon the spot 
centers. 

These spots may destroy the greater part of the green 
tissue of the leaf and its value to the plant as a sugar pro- 
ducer, or even cause the leaves to die, in which event they 
blacken and remain standing nearly upright upon the 
crown. The death of the older leaves causes the crown 
to elongate, suggesting the name " pineapple disease.' ' 
Dry weather followed by a damp spell most favors the 
disease. 

Sprayed plants in New Jersey 1 gave a much cleaner 
foliage and yielded 480 pounds of root as against 380 
pounds from the unsprayed plants from an equal area, a 
gain of nearly 26 per cent. The spray used was Bordeaux 
mixture, 5-5-50, applied first when the plants were six 
weeks old and subsequently at intervals of ten days for ten 
sprayings. 

Root rot, rhizoctoniose (Rhizoctonia betce'Kuhn). — Beets 
affected with this rot usually first show disease at the 
bases of the outer leaves, which turn black. The stalks 
weaken and allow the leaves to fall prostrate, though they 
do not lose their color at once. The disease thence passes 
into the crown, turning the attacked parts brown and later 
leading to cracking of the root. In this condition the my- 
celium of the fungus is clearly evident in the cracks. 
Eventually the whole top may rot off. The disease spreads 
rapidly from plant to plant in the field. Dry or cold 
weather may so retard the disease that the plant can 
recover if not too badly affected. 

The disease is probably the same that has been destruc- 

1 Halsted, B. D., N.J. Agr. Exp. Sta. Bui. 107, p. 10, January 10, 1895. 



208 



DISEASES OF ECONOMIC PLANTS 



tive to sugar beets in Germany. It has been reported from 
several places in the United States. 

Air-slaked lime, 60 to 70 bushels per acre, has been 
recommended. 

Scab (Oospora scabies Thaxt.). — This scab resembles 
closely the scab of the Irish potato and is caused by the 
same fungus. 1 It usually covers more completely the sur- 




Fig. 94. — ■ Potato scab on beets. 

face of the beet than in, the case of the potato, and tends 
more to form corky growths upon the surface than to make 
deep cavities. Usually the corky growth takes a brown color 
which frequently penetrates to some depth into the beet. 

Beets should not be grown upon land known to be in- 
fected with the potato scab or to have borne a badly in- 
fected crop of beets. See also potato scab. 

Soft rot, bacteriose (Bacterium teutlium Met.). — Soft 
rot described by Met calf 2 in 1904 is prevalent in Nebraska 
and in many other states where beets are grown. 

1 Bolley, H. L., N. Dak. Agr. Exp. Sta. Bui. 4, December, 1891. 

2 Metcalf, H., Neb. Agr. Exp. Sta. Rpt. 17, p. 69, 1904. 



VEGETABLE AND FIELD CROPS 209 

It consists of a rotting away of the lower portion of the 
root, the crown and leaves remaining normal except in 
the most severe cases, when the outer leaves may fall. The 
rotted portion is honeycombed with cavities which are filled 
with a viscous, colorless, sour-smelling fluid which exudes 
on pressure. The decayed tissue is usually yellowish gray. 
The rot seldom appears above the surface of the ground. 
Young beets are not susceptible. 

The disease is favored by damp surroundings, as poorly 
drained soil. In some cases large damage is known to 
result, sometimes fully 90 per cent of the crop being affected. 

It is inadvisable, if the disease is noted, to grow beets in 
wet soil. 

Leaf spot (Pseudomonas sp.). — The leaves in this dis- 
ease bear irregular, dark brown or black spots, 1 mm. to 
3 cm. in diameter, chiefly upon the petiole, midrib, and 
larger veins. Occasionally the discoloration extends along 
a vein for some distance, and the tissue on either side 
becomes brown and dry. 

The disease was first observed by Townsend in Utah 
and Colorado, and its bacterial origin was demonstrated 
by Nellie Brown. 1 

Rust (Uromyces betce (Pers.) Kiihn). — Rust has 
long been known in Europe, where it was studied as 
early as 1869. It is occasionally met in some of the 
western states. Though not serious, it has been reported as 
injuring the beet in market gardens in California. It is 
recognized by the characters of the true rusts, i.e. blister- 
like sori, consisting of pustules of spores under the skin. 
With the rupture of the skin the rusty pulverent mass of 

1 Brown, Nellie A., Sci. n. s. 29, 915, June 4, 1909. 



210 DISEASES OF ECONOMIC PLANTS 

spores is uncovered. As in the case of the asparagus rust 
there are three stages, — spring, summer, and winter. 

Removal of the leaves bearing the spring stage and spray- 
ing with Bordeaux mixture has been recommended. Af- 
fected leaves used as feed may carry the disease through 
the manure to plants of the following season. 

Root rot, phomose (Phoma betce Rostr.). — Upon the roots 
a shrunken, coal-black discoloration, extending sometimes 
quite to the center, indicates the presence of this dry rot. 
No disagreeable odor attends the rot. Upon the affected 
surface pycnidia appear as very minute pustules. Upon 
the leaves this same fungus forms large circular dead spots. 

All infected leaves should be removed from the roots 
before placing in storage. 

White rust (Albugo bliti (Biv.) Ktz.). — The white rusts 
are in some aspects similar to the true rusts, but they are 
always white, never rusty or black in color. The sori are 
blister-like, as in the true rusts. The rupture of the 
epidermis releases masses of snow-white spores. 

This disease is seldom of serious import, and ho preven- 
tive measures have been recommended. Should it become 
troublesome, clean culture will be necessary. The same 
disease occurs upon the pigweeds (Amaranthus), which are 
botanically close kin to the beet. 

Damping off. — Damping off of seedlings near the surface 
of the ground soon after they come up, often before thin- 
ning, is a frequent cause of loss. The leaves yellow, 
the roots turn brown, and the plants topple over and die. 
This is in some instances due to the usual causes of damp- 
ing off, p. 60; sometimes to a heavy crust formed upon the 
soil, thus preventing the safe emergence of the seedling. 



VEGETABLE AND FIELD CROPS 



211 



CABBAGE 

Black rot (Pseudomonas campestris (Pamm.) E. F. 
Smith). — Not only does black rot destroy the crop of the 
year, but since its causal germ remains in the soil, it seri- 
ously endangers, if it does not quite prohibit, the subse- 
quent use of the same 
field for susceptible 
crops. Its damage in 
a single season in two 
counties in Wisconsin 
was estimated at be- 
tween $50,000 and 
$60,000. A large per 
cent of the damage to 
cabbage in storage is 
also attributable to this 
disease. Cabbage, kale, 
rape, broccali, kohl- 
rabi, Brussels sprouts, 
collards, turnips, ruta- 
bagas, radish, black 
mustard, charlock, and 
other members of the 
cress family are affected. 

It was first noted in 
1895 l in Wisconsin, and has since proved very disastrous 
in its effects in practically all sections of the United States. 

The first sign of the disease appears upon the edges of 
the leaves as a blackening of the veins. The affected region 




Fig. 95. — Cabbage leaf showing an incipient 
stage of black rot. The disease, which enters 
at the ends of the veins, is progressing toward 
the base of the leaf. After Stewart and 
Harding. 



1 Proc. Amer. Assoc. Adv. Sci. 1895, p. 
Sta. Bui. 65, p. 10, February, 1898. 



93; cited in Wis. Agr. Exp. 



212 



DISEASES OF ECONOMIC PLANTS 



rapidly enlarges, the blackening extending toward the stalk, 
and throughout the system of veins. Soon this blackening 
reaches the stem of the plant and proceeds up and down 
the stem, thus gaining entrance to other leaves, and finally 
reaching the entire plant. Usually many leaves are in- 
fected simultaneously. 
Affected leaves soon 
yellow and wilt, owing 
to the obstruction of 
the water channels, then 
dry, become parchment- 
like, and fall to the 
ground. General infec- 
tion of the plant is fol- 
lowed by death. Other 
rots may supervene, 
giving offensive odors. 
If plants with the small- 
est amount of disease 
are placed in storage, 
the disease continues 
to develop, resulting in 
complete loss. 

Reliable diagnostic 
characters are the blackened vein areas of the leaf, black- 
ened veins as seen in cross sections of the leaf stalk or of 
the stem of the plant. 

Infection arises from the causal bacteria which are often 
present in the soil from preceding years. These bacteria 
gain access to the drops of water at the water pores on the 
leaf edge. Hence they enter the plant and parasitize it. 




Fig. 96. — Portion of cabbage stem showing 
blackened veins. Redrawn after Russell. 



VEGETABLE AND FIELD CROPS 213 

The bacteria may also travel upon seed from diseased 
localities, infect the young plants, and initiate an epidemic 
in a new locality. Diseased plants shipped across the 
country also carry infection. 

The disease may be carried from field to field in any 
diseased plant part or in infected soil, upon tools, feet, etc., 
and especially in manure that has become infected by the 
use of diseased plants as cattle feed. To avoid carrying 
the disease to near-by fields all the precautions suggested 
under soil diseases must be employed. 

It has as yet been impossible to kill the bacteria in the 
soil. The only recourse is such crop rotation as will avoid 
the planting of any susceptible crop upon infected soil for 
a period of several years. Just how long the bacteria can 
remain alive in the soil is not known. In practicing crop 
rotation for elimination of this pest all cruciferous weeds, 
mustard, shepherd's purse, etc., must be avoided, since 
they are susceptible and harbor the disease just as effec- 
tively as would cabbage. 

Since the seed may bear the bacteria, it is well to soak 
them for fifteen minutes in corrosive sublimate one part, 
hydrochloric acid two parts, water one thousand parts, or in 
formalin one pound to thirty gallons of water, to kill these 
germs and thus avoid introducing the disease into new 
localities. If this had been done, many counties now so 
infected as to prohibit cabbage culture would still be free 
from this pest. 

Club root (Plasmodiophora brassicoe Wor.). — Club root 
is widely known, very destructive, and easy of recogni- 
tion. It consists of a greatly enlarged growth of the root, 
either the main root or the lateral roots, or both, as is 



214 



DISEASES OF ECONOMIC PLANTS 



shown in the accompanying figure. It cannot be con- 
founded with any other disease unless it be that caused by 
eel worms (nematodes), and from this it may be easily dis- 
tinguished by the greater magnitude of the club-root galls. 

These enlargments may 
be noted in the seed bed, 
though they are usually 
overlooked until they be- 
come larger in the field. 
They so diminish the vigor 
of the plant that it assumes 
a sickly appearance, ceases 
to develop, and fails to 
head. The affected parts 
usually succumb to offen- 
sive secondary rots, the 
causal organism is released, 
and the soil is thus infected. 
The proof of the parasitic 
origin of this disease was 
made by Woronin in 1873, 
after three years of inten- 
sive study. 

In general the precautions 
against its spread are those 
suggested under the general heading soil diseases. All 
diseased refuse is infective, as is also manure to which it 
has had access. Fields which are diseased remain so for 
several years; therefore rotation to nonsusceptible crops 
should be followed. Seedlings should be examined care- 
fully to guard against the use of plants from an infected 




Fig. 97. — Cabbage club root. Original. 



VEGETABLE AND FIELD CBOPS 215 

seed bed, and special care should be taken to avoid infecting 
the seed bed with soil, manure, or refuse. Air-slaked stone 
lime, 75 bushels per acre, applied each year some weeks be- 
fore planting, has given beneficial results. In New York, 
where 90 bushels of shell lime were applied per acre, an ex- 
cellent crop was grown, while upon untreated soil only 60 
heads were cut from 472 plants. 1 

Club root occurs upon cabbage, kale, cauliflower, turnip, 
rutabaga, collards, Brussels sprouts, radish, stocks, candy- 
tuft, sweet alyssum, and upon wild cruciferous plants, 
shepherd's purse, peppergrass, penny cress, black mustard, 
charlock, false flax, hedge mustard. 

Alternariose (Alternaria Brassicoe (Berk.) Sacc). — 
This disease is described under collard. Upon the cab- 
bage, particularly in the South, it is quite destructive, 
both in the field and in storage. 

Sclerotiniose (Sclerotinia Libertiana Fckl.). — This mal- 
ady is thoroughly discussed under lettuce. Upon the 
cabbage it may be recognized by the cotton-like myce- 
lium and the black sclerotia which appear in advanced 
stages of disease. 

A form of this rot is described by Hedgcock 2 as closely 
resembling black rot, except that it is more watery. Often, 
too, the petioles rot away at the base and the leaves droop. 
Sclerotia are often found. 

Downy mildew (Peronospora parasitica (Pers.) DeBy.). 
— The downy mildew produces the characteristic downy 
patches of sporophores upon the lower surface of the 
leaves, much as is the case of the grape. Seen from above 

1 N.Y. (Geneva) Agr. Exp. Sta. Rpt. 14, p. 528. 

* Hedgcock, G. G., Mo. Bot. Gard. Rpt. 16, p. 149, 1905. 



216 



DISEASES OF ECONOMIC PLANTS 



the diseased spots are angular, limited by the veins, pale 
yellow, and the tissue is somewhat shrunken. 

The disease is common to cabbage, collards, cauliflowers, 
turnips, radish, and many other numbers of the cress 

family. It has been re- 
ported in several states, 
notably Ohio, New Jer- 
sey, New York, Dela- 
ware, Maryland, South 
Carolina, North Caro- 
lina, West Virginia. 
Though it is seldom of 
importance in the field, 
it occasionally does 
damage in the seed bed. 
Spraying the seed bed 
with Bordeaux mixture 
will hold the disease in 
check. Diseased plants 
should be destroyed by 
fire as soon as the bed 
has been used. 

Powdery mildew. 
See turnip. 

Soft rot. See cauli- 
flower. 

(Pers.) Ktz.). — This 
to that described 




Fig. 98. 



- Seedling cabbage plant spotted with 
downy mildew. Original. 



White rust (Albugo Candida 
white rust is similar in appearance 
upon the beet. It has not often been reported as a pest. 

Wilt, fusariose (Fusarium sp.). — This wilt of cabbage, 
commonly known in the South as yellow sides, is very 



VEGETABLE AND FIELD CROPS 217 

destructive through a large territory, particularly in the 
Southern States, and at least as far north as Ohio. 

The chief symptom is yellowing and falling of lower 
leaves, and eventually all of the leaves except those of the 
head. This character may be strongly emphasized 
upon one side or even upon one side of single leaves. 
Affected plants are retarded in growth and often die. After 
death abundant pink acervuli are seen. 

In treatment the same methods should be followed that 
are suggested for cabbage black rot; especially should af- 
fected land be avoided, and the young plants grown in 
healthy soil. 

CANTALOUPE AND MUSKMELON 

Leaf blight (Alternaria Brassicce (Berk.) Sacc. var. 
nigrescens Pegl). — The leaf blight and downy mildew are 
the most destructive diseases of the cantaloupe and musk- 
melon in this country. In Florida, in some seasons, nearly 
the whole commercial crop is lost. Much damage has been 
reported from Ohio, Indiana, and Colorado. 

The leaf blight begins as small round brown spots usually 
marked by concentric rings. In the centers of these spots 
the hyphse develop a moldlike growth. The spots en- 
large to a centimeter or more, coalesce, dry, and cause the 
leaf to curl and shrivel at the margin. The petioles and 
veins are also affected. The ripening of the melons is 
hastened, but the quality is destroyed, the fruit becoming 
soft, wilted, insipid, and valueless. 

If melons be repeatedly grown upon the same field, the 
disease increases year by year; hence rotation should be 
practiced, and resistant varieties should be used. A 



218 



DISEASES OF ECONOMIC PLANTS 



promising resistant variety has been reported by Blinn. 1 
Spraying as recommended for cucurbs is effective. 

Downy mildew (Peronospora cubensis B. & C). — This 
disease is described under cucumber. It is widespread and 
constitutes one of the most serious cantaloupe diseases. 




Fig. 99. — Cantaloupe showing complete death of vines attacked by leaf blight. 
After Blinn. 



Wilt, fusariose (Fusarium vasinfectum Atk. var. nivea 
E. F. Smith) . — Under watermelon this wilt is sufficiently 
discussed. It is not nearly so frequently met as the 
bacterial cantaloupe wilt. See below. 

Wilt, bacillose {Bacillus tracheiphilis E. F. Smith). — 
With the cucumber and squash, as with the watermelon, 
the wilt is serious. The attack in first stages causes the 

1 Blinn, P. K., Col. Agr. Exp. Sta. Bui. 104, November, 1905. 



VEGETABLE AND FIELD CROPS 



219 



vine to droop throughout its length. This is followed by- 
death. The infection is spread by insects also through 
diseased soil. 

The disease has been reported from many states, — among 
them Nebraska, Wisconsin, Maryland, Massachusetts, 
Indiana, — and is presumably present in many others. 




Fig. 100. — The Pollock cantaloupe vine3 adjacent to those shown in Fig. 99, show- 
ing complete resistance to the leaf blight. After Blinn. 

Spraying with Bordeaux mixture, while beneficial in 
retarding the development of other diseases, by repelling 
insects, also lessens the spread of this wilt. Diseased vines 
should be pulled and burned, rotation practiced, and in 
general the suggestions given under soil diseases should be 
followed. 

Anthracnose (Colletotrichum lagenarium (Pass.) Ell. & 
Halst.). — This is a serious pest of the cantaloupe in 



220 



DISEASES OF ECONOMIC PLANTS 



many states. From 50 to 100 per cent damage was reported 
from Nebraska in 1905. The disease is discussed under 
watermelon. 

Southern blight (Sclerotium Rolfsii Sacc. in litt.). — 
A large percentage of the cantaloupe crop in the southern- 




Fig. 101. — Leaf spotted with downy mildew. Original. 



most states is often destroyed by this disease. It is par- 
ticularly noticeable on fruit upon the side touching the 
ground, first as a slight rot, followed by a white fringe of 
fungous threads which soon surround the whole fruit. 
Later sclerotia appear as small round bodies, dirty white 
to dark brown. For further description and treatment, 
see pepper. 



VEGETABLE AND FIELD CROPS 



221 



Powdery mildew (Erysiphe polygoni DC). — This mildew 
of the cucumber and cantaloupe in general appearance 
resembles that described for the grape. It is more com- 
mon under glass 
than in the open, 
and here indicates 
too much moisture 
and too little ven- 
tilation. It is sel- 
dom injurious in the 
field. 

Flowers of sul- 
phur applied to 
the hot water or 
steam pipes in the 
form of a paste is 
useful. 

Leaf blight, cer- 
cosporose (Cercos- 
pora Cucurbitce Ell. 
&Ev.). — The spots 
of this disease are 
much like those of 
alternariose, but are 
of lighter brown 
color and more angular form, being limited by the veins. 

Bacillose, rot (Bacillus melonis Giddings). — This soft 
rot was described first by Giddings x as causing 25 per cent 
loss in certain fields in Vermont in 1907. The decay 




Fig. 102. — Sclerotium Rolfsii Sacc. in litt. growing 
upon a cantaloupe at point of contact with the soil. 
After Hume. 



1 Giddings, N.J. Sci. n. s. 
Bui. 148, 1910. 



», 911, June 4, 1909; also Vt. Agr. Exp. Sta. 



222 



DISEASES OF ECONOMIC PLANTS 



usually begins on the lower side of the fruit, resulting in 
shrunken diseased areas over which the skin remains un- 




Fig. 103. 



Muskmelon 65 hours after inoculation with Giddings germ. 
After Giddings. 



broken. The flesh near the infection point becomes com- 
pletely decayed and has an offensive odor. 



VEGETABLE AND FIELD CROPS 



223 



The cause is a bacillus which gains entrance through 
wounds, often through ruptures occasioned by excessively 
rapid growth. 

Spraying with Bordeaux mixture is recommended; also 
turning the melons so as to 
expose all sides to light and 
air. 

Wilt (Mycosphcerella citrul- 
lina (Sm.) Gr.). — This wilt 
seems to be rare, perhaps 
affecting to serious extent 
only greenhouse-grown can- 
taloupes. It is known upon 
watermelon in the field. 

Infection is local at the 
nodes, never at internodes, 
and seems to originate at the 
leaf axil, perhaps due to re- 
tention at that point of the 
water necessary for germina- 
tion of the spores. The edges 
of the infected areas are "oily 
green " in color, often with 
resin-colored, gummy exu- 
date. The older parts are 
either darker and gummy, 
or dry and gray, and bear 
many brown pycnidia. 

The fungus is not killed by winter or by fumigation with 
hydrocyanic acid gas. Spraying with Bordeaux mixture 
after the plants are about half grown, but before the dis- 




Fig. 104. — Portions of muskmelon vine 
showing pycnidia and perithecia of 
Mycosphserella. After Dorsey. 



224 



DISEASES OF ECONOMIC PLANTS 



ease appears and often enough 
thereafter to cover growing 
parts, is recommended. 1 

Phyllostictose (Phyllosticta 
cucurbitacearum Sacc . ) . — This 
leaf spot has been destructive 
in several states, notably so in 
New Jersey and Ohio. The 
spots are light colored and the 
fungus appears as a pycnidium 
in their centers. 

Cladosporiose. See cucumber. 

CARROT 

Soft rot, bacillose (Bacillus 
carotovorus Jones 2 ). — In Ver- 
mont serious loss from rotting 
of carrots was reported to the 
Experiment Station in 1898. 
Investigation by Jones showed 
it to be due to bacteria and that 
numerous other crops, namely, 
turnip, rutabaga, radish, salsify, 
parsnip, onion, celery, hyacinth 
leaves, and' the fruit of tomato, 

eggplant, and pepper were susceptible to the same disease. 

Cauliflower, Irish potato, sweet potato, beet, and asparagus 

were not susceptible. 

1 Grossenbacher, J. G., N.Y. (Geneva) Agr. Exp. Sta. Tech. Bui. 9, 
February, 1909. 

2 Jones, L. R , Vt. Agr. Exp. Sta. Rpt. 13, 299, 1901 ; also N.Y. (Geneva) 
Agr. Exp. Sta. Tech. Bui. 11, 1910. 




Fig. 105. — Carrot showing 
rot ; shaded portions represent 
the rotted part of the root. Re- 
drawn after Jones. 



VEGETABLE AND FIELD CROPS 225 

Rot begins in the field, but becomes serious during stor- 
age. The initial attack is either at the crown or root tip, 
from which points it proceeds rapidly through the core, 
which becomes softened and somewhat browned with a 
rather, sharp boundary between diseased and healthy tis- 
sue. 

Fields known to be infested should be relieved of sus- 
ceptible crops by suitable rotation. Manure, which may 
have become infected in any way, e.g., by feeding diseased 
crops to stock, should be avoided. Drying of the roots 
kills the causal organism, as does also exposure to sunlight. 
Drying in the light is therefore equivalent to surface dis- 
infection and serves to reduce the damage. Storage below 
10° C. (50° F.) gives best results. 

CAULIFLOWER 

Black rot, pseudomonose (Pseudomonas campestris 
(Pamm.) E. F. Smith). — This disease affects the cauliflower 
in much the same way as it does the cabbage. Local 
infection in the head often produces the effect shown in 
Fig. 106. For discussion of symptoms and treatment, 
see cabbage. 

Sclerotiniose. See cabbage. 

Soft rot, bacillose (Bacillus oleracea Harr.). — A soft 
rot affecting cauliflower, cabbage, and turnips, and in 
some cases destroying as much as 64 per cent of the crop, 
is described by Harrison. 1 The disease may be identical 
with the soft rot of carrot. 2 

1 Harrison, F. C, Ont. A. C. & E. F. Bui. 137, August, 1904. 

2 Harding, H. A., Jones, L. R., and Morse, W. J., N.Y. (Geneva) Agr. 
Exp. Sta. Tech. Bui. 11, 1910. 

Q 



226 



DISEASES OF ECONOMIC PLANTS 



CELERY 

Leaf spot, early blight, cercosporose (Cercospora Apii Ft.). 
— The leaf spot is common in both Europe and America, 
constituting probably the most destructive disease to 
which the celery plant is subject. It is known from 







Fig. 106. — Cauliflower affected with black rot. 
(Pseudomonose) . Original. 

Colorado to New Jersey. In Florida in 1906 it is said to 
have injured 80 per cent of the crop. The crop is largely 
reduced, and the unsightliness of the spots injures the 
salability of the product. 

The spots appear first upon the outer, older leaves as 
pale yellowish regions, showing from both sides of the leaf. 
They are irregular with slightly raised border and are 



VEGETABLE AND FIELD CROPS 227 

angular in outline, owing to their limitation by the veins. 
They seldom exceed 3-6 mm. in diameter unless by the 
coalescence of several spots. The spots soon become brown, 
and the central part turns ashen-white and is seen by the 




Fig. 107. — Cercosporose of celery. Original. 

aid of a hand lens to bear numerous hyphse. The leaves 
may bear so many spots as to appear as though scorched, 
and often death results to the entire plant. 

The disease spreads most rapidly in damp warm weather. 

Marked difference in varietal resistance was reported by 
Tracy 1 as early as 1885, the Boston Market and Golden 

iSee Lamson-Scribner, F., U.S. Dept. Agr. Rpt. for 1886, p. 117. 



228 DISEASES OF ECONOMIC PLANTS 

Heart suffering much, while the White Plume was but 
slightly injured. 

All plants showing a trace of disease should be rejected. 
Healthy plants from infected lots may with advantage be 
dipped in Bordeaux mixture to cleanse them of adhering 
spores. Spraying with ammoniacal copper carbonate or 
Bordeaux mixture is effective. Treatment should be begun 
before the disease appears, i.e., in the seed bed, and con- 
tinued at ten-day to fourteen-day intervals, throughout the 
growing period. All spore-bearing refuse should be burned. 

Leaf spot, late blight, septoriose (Septoria Petroselini 
Desm. var. Apii Br. & Cav.). — In Italy late blight was 
first reported in 1890; in the United States in 1891. 
A loss of 1950 carloads and a money loss of $550,000 was 
estimated in California in 1908. 

In its beginning it consists of leaf spots very like those 
of the last disease, though more irregular and indefinite in 
boundary. In later stages, the infection of the leaf becomes 
general, numerous black pycnidia are scattered upon all 
parts of the leaf and even upon the blanched petioles, 
which through their unsightliness injure the salability of 
the crop. In extreme cases wilting of the leaves and de- 
struction of the plant follows. After the celery is put 
in storage the disease may still progress and do great 
damage, rotting off the leaves and forcing early marketing. 
This disease is often found in the seed bed, and is prob- 
ably carried by the seed, since the pycnidia are abundant 
upon the seeding stalks and fruit. If the disease has 
been troublesome in preceding years, the plants in the seed 
bed should be sprayed with Bordeaux mixture as soon 
as they are above ground, and once or twice a week there- 



VEGETABLE AND FIELD CROPS 229 

after until transplanted. If the disease develops in the 
field, the crop should be sprayed with Bordeaux mixture 
at ten-day intervals. 

To minimize loss during storage no diseased plants 
should be stored. If storage is imperative, badly infested 
leaves should be picked off, and in extreme cases the plants 
should be dipped in a fungicide (ammoniacal copper car- 
bonate) before they are stored away. 

Leaf spot, phyllostictose (Phyllosticta Apii Halst.). — 
This leaf spot begins as a dull brown patch and never 
becomes the light ashen color of the cercosporose spot. 
The spots, too, are not angular, as in the latter disease, and 
are fewer in number and larger. They usually begin at 
the leaf edge. In older spots pycnidia are apparent. 

Center blight, soft rot (Bacteria). — A soft, light brown 
rot of the central bud, sometimes of the leaf or leaf stalks, 
is characteristic of a disease which is probably bacterial; 
possibly nearly related to the carrot soft rot. 

Rust (Puccinia bullata (Pers.) Wint.). — This true rust 
has not yet been destructive in America. It may be 
recognized from its sori, which resemble those of the as- 
paragus rust. 

Damping off due to Sclerotinia (see lettuce), Rhizoctonia 
(see p. 61), and Fusarium have caused much loss in the 
South. See also p. 63. 

COLLARD 

Black rot. See cabbage. 
Wilt, bacillose. See cabbage. 
Club root. See cabbage. 
Downy mildew. See cabbage. 



230 



DISEASES OF ECONOMIC PLANTS 



Black mold (Alternaria Brassicce (Berk.) Sacc). — The 
affected spots are nearly black, marked concentrically, 
are circular, and are not definitely bordered, i.e., they 
shade off gradually into the surrounding healthy tissue. 




Fig. 108. 



■ Collard black mold as seen from upper side of the leaf. 
Original. 



They enlarge sometimes to 2-3 cm. in diameter. The 
tissue dries, becomes brittle, and often falls away, leaving 
ragged holes. 

The general appearance of the spot as seen from above 
is pale green; as seen from the lower surface, shown in 
Fig. 108, it is densely black, strongly contrasting with 



VEGETABLE AND FIELD CROPS 231 

the white spots of the downy mildew which may occur in 
association with this disease. The damage may be very 
great, in many instances resulting in the death of the plants 
or complete loss of their usefulness. 

CUCUMBER 

Downy mildew (Pseudoperonospora cubensis B. & C.) Ros- 
ten. — This downy mildew first shows its presence by yel- 
lowish angular spots 3-6 mm. in diameter upon the leaves as 
seen from above. These appear first upon the older leaves at 
the center of the plant. The spots become more distinct, 
enlarge, increase in number, and soon the whole leaf be- 
comes pale, sickly, and dies. If the weather is moist, the 
characteristic white hyphse and spores tinged with purple 
may be seen on the undersides of the older spots. The 
disease progresses to the younger leaves, slowly in dry or 
cool weather, but very rapidly in warm, wet weather. 
The field is soon reduced to a mass of dry dead leaves. 

The mildew was first described in 1868 from Cuba. In 
1889 it suddenly attracted attention in the United States 
(New Jersey, Florida, and Texas) and in Japan. Since 
that time it has been destructive in many states. The loss 
in Wayne County, Ohio, alone was estimated at $45,000 
in one season. 

It grows upon cantaloupes and cucumbers in most de- 
structive form and is injurious to squashes, pumpkins, 
watermelon, gourds, and other cucurbs. The fungus 
winters out of doors in the South and in the greenhouse 
in the North and spreads thence to the fields annually if 
weather conditions are favorable. 

This disease is often injurious to cucumbers under glass 



232 



DISEASES OF ECONOMIC PLANTS 



as well as in the field. It is well to sulphur the greenhouses 
thoroughly when empty and to clean and whitewash 







Fig. 109. — Spots of downy mildew upon cucumber leaf. After Orton. 

all walls and wood in order to kill any fungi present. 
Should the disease appear, spray at once as in field practice. 
For direction for field spraying see cucurb spraying. 

Anthracnose (Colletotrichum lagenarium (Pers.) Ell. & 
Halst .) . — Upon the cucumber leaf this disease makes circular, 



VEGETABLE AND FIELD CROPS 233 

not angular, spots which, instead of yellowing, turn brown, 
die, and often tear. Upon the stems it forms elongated 
light brown spots, and on the fruit sunken spots much like 
those upon the watermelon. Twenty-five to sixty per 
cent injury has been estimated in New Jersey, and $10,000 
to $15,000 damage has been reported from a single county 
in Nebraska. This disease is more fully described under 
watermelon. 

It is especially bad under glass. The treatment is as 
for the downy mildew, see above. In the field, spraying 
has proved effective. 

Wilt, bacillose. See cantaloupe. 

Wilt, fusariose. See watermelon. 

Phyllostictose. See cantaloupe. 

Cercosporose. See cantaloupe. 

Sclerotiniose, timber rot (Sclerotonia Libertiana Fckl.). — 
Upon cucumbers under glass this disease occasions serious 
loss. It is rare out of doors. The first indication of the 
disease is the appearance of a dense mass of white myce- 
lium near the nodes of the stem which is still green. As 
the disease progresses the stem shrinks and yellows, the 
softer parts decay, and the stem finally dries up. In the 
interior of sick stems the white mycelium may also be 
found, and later near the nodes smooth, slender, black 
sclerotia. Sclerotia are also sometimes found on the ex- 
terior of the stem in the mycelial masses. The germina- 
tion of the sclerotia, described under lettuce sclerotiniose, 
results in immense numbers of spores. These falling upon 
dead cucumber tissues grow upon it and form a mycelium 
which attains such vigor as to enable it to attack healthy 
tissue and rapidly destroy it. 



234 DISEASES OF ECONOMIC PLANTS 

To control this disease all infected plants should be 
destroyed by fire before they have had opportunity to 
form sclerotia, and the place from which they are taken 
sprayed with a heavy application of some fungicide. 

Damping off. See p. 60. 

Powdery mildew (Erysiphe polygoni DC). — This mildew 
has the general characteristics of the powdery mildews, a 
whitish flourlike coating upon the leaves and stems; at 
first in circular spots, but later diffuse. Its presence in 
America was first announced by Humphrey. 1 It has 
since been frequently reported in the field and occa- 
sionally under glass. The fungus appears chiefly upon 
the upper surfaces and is most developed upon the older 
leaves. It renders the fruits bitter and distorts them. 

The disease is not usually serious. If it is so under 
glass, the treatment suggested under cantaloupe will be 
found effective. 

Leaf blight, fruit spot (Cladosporium cucumerinum Ell. 
& Arth.) . — This spotting of the fruit was first noted at 
Geneva, N.Y., in 1887, 2 where it was so abundant as to 
ruin the crop for pickling. In 1905-1906 in Wisconsin it 
caused abandonment of several pickle factories. 

The spots begin when the fruit is only 2-5 cm. long, 
as gray, slightly sunken places with minutely velvety sur- 
faces. They are about 3 mm. in diameter, but coalesce 
into irregular patches, particularly toward the flower end. 
As the spots age they darken to greenish black, and a 
gummy exudate often appears. 

Upon leaves where injury is more rare than upon the 

1 Humphrey, J. E., Mass. Agr. Exp. Sta. Rpt. 9, p. 222, 1892. 

2 Arthur, J. C, N.Y. (Geneva) Agr. Exp. Sta. Rpt. 316, 1887. 



VEGETABLE AND FIELD CROPS 235 

fruit the spots are at first watery and translucent; later 
the leaf wilts, and is soon reduced to a rotten mass. The 
disease progresses so fast that a plant may be practically 
destroyed in a few days. Immediate and thorough spray- 
ing may- be of service. 

Acremoniose (Acremonium 1 sp.). — In this disease 
shoots are stunted, fruits deformed, and leaves yellowed 
and killed. Upon the lower leaf surfaces a delicate white, 
glossy film like dried albumen is seen. This is in reality 
a web of fungous threads. Plants that are attacked may 
put forth new vigorous shoots to survive for a time, then 
die. The disease has been known to reduce the yield 90 
per cent. No treatment has been advocated. 

Cucurb Spraying 2 

Planting should be at such distance as to facilitate 
machine spraying ; that is, relatively close in the row, but 
with the rows wider apart than is usual in most sections 
of the country. In cultivating, the vines should be induced 
to spread along the row, and by the use of a vine turner a 
one-foot open alley should be maintained throughout the 
season for the wheels of the sprayer. 

Geared sprayers with proper length of axles to cover 
one row may be used, and three rows may be sprayed at 
one time. Particular attention must be given to reaching 
the undersides of the leaves with the spray. Spray first 
when the vines begin to run, using Bordeaux mixture 

1 Humphrey, J. E., Mass. Agr. Exp. Sta. Rpt., pp. 227-228, January, 
1892. 

2 Orton, W. A., U.S. Dept. Agr. Farmers' Bui. 231, 1908. 



236 DISEASES OF ECONOMIC PLANTS 

3-6-50. For subsequent sprayings use 4-4-50 Bordeaux 
at intervals of about ten days if the weather is dry; 
oftener, if growth is rapid. 

The cost of six applications is placed at $5.22 per acre, 
including labor. The net profits from this have been as 
high as $163.50 per acre. 

EGG PLANT 

Wilt, bacillose (Bacillus solanacearum E. F. Smith). — 
This disease is closely like the wilt described for the 
tobacco, and the remarks made in that connection con- 
cerning cause, spread, and treatment apply to this crop 
plant as well. 

Wilt, nectriose (Nectria Ipomoece Halst.). — Unlike so 
many diseases there is no leaf or fruit spot whatever, 
though whole fields have been so badly attacked that 
scarcely a fruit was gathered. The affected plants when 
half grown take on a yellowish, sickly appearance, the 
foliage wilts, the lower part of the stem becomes coated 
with a whitish mold, and the plant usually dies. Nu- 
merous small pink perithecia are found upon the stem just 
below, or at the surface of the ground. 

This disease is close kin to the wilt of cotton, and most 
that is said there regarding treatment applies here. 

Damping off (Pythium DeBaryanum Hesse, and Phoma 
Solani Halst.). See p. 61. 

Leaf spot, phyllostictose (Phyllosticta hortorum Speg.). — 
Plants in the hotbed are subject to leaf -spot attack, 
the transplants dying, or it may appear later upon leaves 
arid fruit and result only in more or less serious leaf spots. 

Upon the leaf large irregular brown or gray patches are 



VEGETABLE AND FIELD CROPS 237 

produced. Here numerous black pycnidia appear, and later 
the leaf becomes torn. Upon the fruit are large sunken 
spots of similar appearance. 

Treatment with Bordeaux mixture or ammoniacal cop- 
per carbonate before transplanting is recommended, fol- 
lowed by similar spraying in the field. Eight sprayings 
with Bordeaux mixture in one test yielded 100 fruits, while 
a similar plat but unsprayed gave only about half as many. 
Clean culture should be followed. 

Gray mold (Botrytis fascicular is (Cda.) Sacc). — In this 
rot the purple fruits assume a tan color in blotches, followed 
by softening of the tissue and rapid development of a gray 
mold; the fruit in the meantime changing into a com- 
pletely rotten mass. 

Anthracnose, glceosporiose (Gloeosporum melongence Ell. 
& Halst.). — Pits appear upon" the fruits, and in these the 
pink-tinted acervuli. 

Blue mold (Penicillium sp.). — This rot is very similar to 
blue mold of apples. 

Leaf spot, ascochytose (A scochyta Lycopersici Brum). — 
This fruit spot is very similar to that of phyllostictose.^ 

GINSENG 

Blight, alternariose (Alternaria panax Whet. 1 ). — Brown 
cankers upon the stem and watery spots in the leaf, often 
involving the entire top of the plant, mark this disease. 
Badly blighted plants appear as if drenched with boiling 
water. 

It is a serious menace to the ginseng industry of New 
York State, often causing the leaflets of entire beds to be 

1 Whetzel, H. H., Sci. n. s. 29, 912, June 4, 1909. 



238 DISEASES OF ECONOMIC PLANTS 

spotted, depleting the vigor and productiveness of the plants. 
The seed crop is sometimes completely lost. It can be 
controlled by thorough spraying. Use copper sulphate, 
1 pound to 10 gallons, before the plants come up, thor- 
oughly soaking the soil; then Bordeaux mixture 5^-50 
as soon as the plants come up, and repeat every other day 
during the first few weeks, less often later. The mixture 
will adhere better if 2 pounds resin, 1 pound sal soda, and 
1 gallon of water, boiled together until clear brown in color, 
be added. 

Wilt, fusariose (Fusarium vesinfectum Atk.). — The most 
disastrous ginseng disease in the West is the wilt described 
by Reed, 1 which caused destruction, in Missouri, of whole 
plantations in a single week. With the first symptom of 
attack the leaflets droop, yellow, and die; then the entire 
leaf dies to the base, drys up, and falls off. The immature 
seeds shrivel and fail to mature. The dead, black stem 
alone remains standing. The roots are not killed, but the 
season's growth is ended, and the buds to produce the next 
season's growth are dwarfed. Secondary decays, soft rots, 
may follow. 

The cause of this disease is said to be the same as that 
of the watermelon wilt, and remarks made in that con- 
nection as to its habits, spread, etc., apply here also. 

It is claimed that the wilt fungus cannot attack ginseng 
plants unless they are previously weakened by the inroads 
of some other parasite. Prevention of other diseases 
therefore renders the wilt harmless. Thorough spraying 
for all diseases affecting this crop is thus doubly important. 
Diseased plants should be removed and burned. 

1 Reed, H. S., Mo. Agr. Exp. Sta. Bui. 69. 



VEGETABLE AND FIELD CROPS 239 

Stem anthraonose (Vermicularia Dematium (Pers.) Fr.). — 
Numerous black scars appear on the stems a few weeks 
after the plants come above ground. These spread and 
sometimes encircle the stems. The leaflets then brown. 
Often the plants fall over, even before they wilt. 

Since the plants are not killed but usually recover, the 
greatest loss lies in the destruction of the seed crop. 

Bordeaux mixture applied about three weeks after the 
plants appear in the spring and each three weeks thereafter, 
until August, more often if the season is wet, will control 
the disease. All dead stalks, leaves, etc., should be 
collected and burned in the fall. 

Wilt, acrostalagmose (Acrostalagmus albus Preuss.). — 
This wilt is due to stoppage of the veins by fungous 
growth, and the chief symptom is wilting of the leaves, 
followed by death of the stem and leaves. Sections of the 
rootstock reveal a yellowing of the water ducts and veins, 
which contrasts strongly with the normal white of a healthy 
plant. This unnatural coloration of the veins may also 
be seen upon stripping the bark from the root lengthwise. 

The disease is largely confined to the older, less vigorous 
roots. It is advisable to remove and dry the infected 
roots and to replace the soil of infected beds with new, 
healthy soil. Soil disinfection should be employed if 
practicable. 

Black rot (Sclerotium sp.). — Black, warty growths (scle- 
rotia) upon the rhizome indicate sclerotiose. The roots 
are very black, but upon drying, bleach somewhat. In 
old age this blackening may extend to the center of the root, 
which becomes wet, spongy, and pliable. The disease re- 
mains in the soil some years after infection. Sick roots 



240 DISEASES OF ECONOMIC PLANTS 

should be removed, and burned if not marketable. Treat 
also as for wilt. 

Soft rot. — This rot occurs widely and causes large loss, 
placing it among the worst ginseng diseases. The root 
decays rapidly, is sticky and ill smelling. The leaves color 
red and yellow and soon die. 

Damping off (Rhizoctonia, etc.) . — Damping off is largely 
avoided by thorough ventilation, and the avoidance of ex- 
cess of moisture in soil and air. Stirring the soil to hasten 
drying aids. See p. 61. 

Leaf anthracnose,pestalozziose (Pestalozziafunerea, Desm.) . 
— A disease more destructive to young plants than to older 
ones is pestalozziose, 1 which appears as a black, velvety 
growth at the bases of the leaves and flower stalks, causing 
them to die and fall off. 

Spray as for alternariose. 

End rot, fiber rot (Thielavia basicola (B. & Br.) Zopf.). — 
This is especially bad upon seedlings, resulting in sudden 
wilting, which causes them to bend over and dry up. The 
fine roots are affected as are the roots of tobacco. 

GOLDENSEAL (Hydrastis) 

Blight (Alternaria sp.). — Spots occur upon the leaves 
The disease seems to be identical with that of ginseng. 

HOP 

Powdery mildew (Sphcerotheca Humuli (DC.) Burr.). — 
This powdery mildew, while serious in many parts of Europe, 
has been seen but rarely on the hop in America, and has 
never been reported as seriously injurious. It is recognized 

1 Reed, H. S., Mo. Agr. Exp. Sta. Bui. 69, October, 1905, 



VEGETABLE AND FIELD CROPS 241 

by the usual characters of the powdery mildews. See grape. 
If it should become troublesome, spraying with Bordeaux 
mixture or ammoniacal copper carbonate must be prac- 
ticed. 

Cylindrosporiose (Cylindrosporium Humuli Ell. & Ev.). 
— Small, rusty brown, angular leaf spots largely limited 
by the veins are present. They show most clearly upon 
the lower sides of the leaves. Minute black acervuli are 
present. 

The disease has been reported from several states, but 
has not been regarded as serious. 

HORSE-RADISH 

Leaf blight, septoriose (Septoria Armoracioe Sacc). — 
Ruin is occasionally brought to a crop by this disease, 
which is nearly always present to some extent. The leaves 
bear numerous circular spots, blanched in the center and 
pale yellow at their borders. Pycnidia are borne in the 
centers of the spots. Badly affected leaves turn yellow 
and become filled with holes caused by the dropping of the 
dead tissue of the spots. 

Ramulariose (Ramularia Armoracice FckL). — This spot 
is much like the septoriose except that no pycnidia are 
present. 

Black mold, macrosporiose (Macrosporium herculeum E. & 
M.). — In late summer the leaf spots of this disease are 
often abundant. They are circular, blanched, and later 
coated with a black mold. The injury does not warrant 
treatment. 

White rust (Albugo Candida (Pers.) Ktze.). — The dis- 
ease is the same as that upon cabbage. It is often pres- 

R 



242 



DISEASES OF ECONOMIC PLANTS 



ent upon horse-radish, but does not usually become 
serious. 

Leaf spot, cercosporose (Cercospora Armoracice Sacc). — 
This spot is much like that of ramulariose. 

LETTUCE 

Sclerotiniose, drop, wilt (Sclerotinia Libertiana Fckl.). — 
The disease begins with wilting of the outer lower leaves, 




Fig. 110, — Sclerotia of Sclerotinia from lettuce germinating. 

which droop and fall flat upon the ground; a similar fate 
rapidly overtakes the inner leaves, and so on over the whole 
plant, until within a few days the entire plant is dead, 
lying flat upon the ground, appearing much as though 
scalded by a dash of hot water. The disease progresses 
with wonderful rapidity, the plants appearing to die in a 
day. 

Upon the undersides and at the bases of the leaves occur, 



VEGETABLE AND FIELD CROPS 243 

at this time, dense, cotton-like growths of mycelium, and in 
later stages small black, irregular bodies, the sclerotia, 
which vary from 3-10 mm. long, somewhat less in thick- 
ness. The sclerotia and the mycelium are unmistakable 
signs of this disease. 

Sclerotiniose was first definitely recognized in America 
in 1900, though it doubtless did much damage before then. 
It has since then followed the rapidly extending lettuce in- 
dustry into many states and is particularly destructive in 
the South Atlantic seaboard states from Virginia to Florida, 
where its inroads upon the crop grown under cover are es- 
pecially damaging. The causal fungus may persist from 
year to year as sclerotia in beds once infected, — beds cost- 
ing originally often $1000 per acre, — and thus destroy 
their value for lettuce culture. The damage is thus much 
more than injury wrought merely to the present crop. 

The fungus passes from one season to the next, as the 
sclerotia which, favorably situated, are capable of germina- 
tion, each producing several trumpet-shaped organs, 
Fig. 110, with stems about 15 mm. long and disks 3-8 mm. 
or less in diameter. Spores capable of initiating the fungous 
growth upon dead or sick lettuce tissue issue in great num- 
bers from these disks, and from material thus infected the 
fungus can make its way into the healthy lettuce plant. 

If all infected plants be pulled and burned as soon as the 
first indication of disease is observed, the formation of 
sclerotia will be prevented. As an additional precaution 
it is well to spray the locus of the diseased plant thoroughly 
with Bordeaux mixture or bluestone solution. 

A few years of such procedure will much reduce the in- 
fection or perhaps eliminate it entirely. All lettuce trash 



244 DISEASES OF ECONOMIC PLANTS 

should be removed from the beds, since it serves as the ini- 
tial point of attack for the fungus. Those who are free 
from the disease should guard against its introduction upon 
diseased refuse in any form. Compost which may be con- 
taminated with lettuce refuse bearing this disease should be 
avoided. Those growing lettuce under glass have found 
soil disinfection effective and practicable. 

Damping off. See p. 60. 

Gray mold (Botrytis cinerea Pers.). — Gray mold is es- 
sentially a leaf disease, beginning usually at the leaf edges, 
and there causing wilted, flaccid patches which soon be- 
come coated with a straw-colored downy fuzz, the sporifer- 
ous hyphse. The whole leaf, usually an outer one, may 
droop and die. 

Weak plants may succumb entirely to such attack, the 
disease passing slowly from the outer leaves toward the 
central ones. In all cases the affected parts after death 
become coated with the dirty fuzzy down characteristic 
of the disease. This disease may be distinguished from 
sclerotiniose by the absence of the white mycelium and 
sclerotia, and by the presence of the gray, dirty, botrytis 
growth which does not belong to sclerotiniose. The two 
diseases, while often occurring separate, may both infect 
the same beds or the same plants. Botryose may also 
cause damping off. 

High temperature, lack of ventilation, and lack of vigor 
in the plant, resulting from improper care, are essentials 
to attacks of botryose. If these be avoided, this disease 
will do no serious harm. 

Rosette (Rhizoctonia sp.). — A moist rot sets in first 
upon portions of leaves which touch the ground, and 



VEGETABLE AND FIELD CROPS 245 

spreads thence throughout the leaves, rotting away the 
blades but leaving the midribs standing, 1 thus distinguish- 
ing this from all other diseases. Infection proceeds from 
leaf to leaf at point of contact, often reaching the center 
of the head,- while the outer leaves are infected only in 
spots. The inner leaves may all be reduced to a slimy 
mass though the outer leaves still remain, surrounding it 
as a rosette. 

Downy mildew (Bremia Lactucce Regel). — This occa- 
sionally destructive mildew shows the character of the 
downy mildews, i.e., downy fuzz below, yellow spots 
above (see grape). It has been reported from Massa- 
chusetts as causing much loss to lettuce under glass, es- 
pecially upon the older leaves. It is also noted upon old 
leaves on seed plants of both cultivated and wild lettuce. 

Close attention to proper cultural conditions in the 
greenhouse, especially as to moisture, ventilation, and 
temperature, usually suffice to hold it in check. Evap- 
orated sulphur also aids in suppressing the mildew. 

Soft rot (Bacteria). — Several different diseases due to 
bacteria occur upon this host. Notable among them is a 
soft rot of the head and a hollowing of the stems. Peculiar 
translucent watery spots upon the leaf are also caused by 
bacteria. 

These diseases have not yet been fully studied nor treat- 
ments suggested. 

Leaf perforation, anthracnose (Marsonia perforans Ell. & 
Ev.). — The most conspicuous character is the perforation 
resulting from the fall of the tissue killed by the attacking 

1 Stone, Geo. E., and Smith, R. E., Mass, Agr. Exp. Sta. Bui. 69, 
September, 1900. 



246 DISEASES OF ECONOMIC PLANTS 

fungus. These perforations are from 1-2 mm., or more, in 
diameter, with irregular borders. Upon the midrib and 
petiole depressed spots result. With small young leaves 
distortion is produced, especially at the apex. The disease 
appears to be limited to greenhouses and to be spread 
largely by watering. 

It was first described by Selby 1 in Ohio in 18.96 and has 
since been noted in other states. 

Blight, septoriose (Septoria lactucce Pass.) and (Septoria con- 
similis E. & M.) . — Upon the old outer head leaves there often 
appear very numerous, black pycnidia, so small as to remain 
unnoticed unless by special search. The injury is usually in- 
significant, though some dwarfing and curling of the leaf re- 
sults. Upon seed plants these same diseases attack the leaves 
with greater vigor, causing pale brown, discolored areas and 
the death of the older leaves. Sometimes, through neglect 
to destroy plants of the seed bed, these diseases may gain 
such foothold as to cause injury in other beds. This can 
usually be avoided by destruction of the seed-bed plants as 
soon as transplanting is over. 

The diseases are not usually troublesome until late in 
the season. The Trianon, Wonderful, and Salamander 
varieties are very susceptible. The Boston is quite resistant. 

MUSHROOMS 

Mycogonose (Mycogone perniciosa Magn.). — Though 
noted in Germany as early as 1887 by Magnus, this disease 
was not called to attention in America 2 until March, 1909. 

1 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 73, December, 1896. 

2 Mrs. Flora W. Patterson, Am. Photopath. Soc, 1st annual meeting, 
Boston, Mass., December 31, 1909. 



VEGETABLE AND FIELD CROPS 247 

French experts detect the disease first in the spawn as 
an abnormal, white, fluffy growth. Later the mycelium of 
the mushroom fails to develop normally, but instead pro- 
duces monstrous soft growths. Whole clumps develop into 
moldy masses', which soon putrify with disagreeable odor. 

Infected beds or houses may be abandoned or cleaned 
thoroughly, then sprayed once or twice with a 2\ per cent 
solution of lysol in water, or with copper sulphate, 1 pound 
to 15 gallons. 

MUSKMELON 
See canteloupe. 

ONION 

Smut (Urocystis Cepulce Frost). — As with the wilt of 
tobacco and cotton, this disease resides in the soil and is 
therefore destructive not only to the present crop, but is 
also prohibitive of successful culture of susceptible crops 
in the future. 

The smut, which seems to have originated upon a wild 
variety of onion, occurs in both Europe and America. It 
was known in Connecticut as early as 1860, Massachusetts, 
Pennsylvania, and Ohio in 1889, later in New York, New 
Jersey, and Delaware, and has since been recorded from 
Iowa and Georgia. The first mention of serious loss by 
onion smut in America was in 1870. Its inroads upon the 
crop are often such as to prohibit profitable onion culture 
unless preventive measures are taken against the disease. 

The smut attacks the very young seedlings through the 
still tender, delicate leaf sheaths. Onions grown from 
sets are immune, and onions from seed, if they pass the 



248 



DISEASES OF ECONOMIC PLANTS 



very young state without infection, are so protected by 
hardening of the outer plant parts that no infection is 




Fig. 111. — Young onion plants showing effect of smut ; at left smutted plants, at 
right healthy plants same age. After Hinman. 

likely to result, even if the bulb be surrounded by thor- 
oughly infested soil. 



VEGETABLE AND FIELD CROPS 249 

Upon the infected seedling's leaves dark opaque spots 
may be noted, especially upon holding the leaves against 
the light. The portions of the leaf above such spots soon 
die, and the spots rupture, exposing sooty, powdery masses. 
Badly infected seedlings succumb early, while others may 
survive until harvest. The disease is more fatal if attended 
by dry weather, which reduces the vigor of the host plant. 
Plants surviving the disease show smut in the outer leaves, 
often also within. Diseased bulbs dry up and rot. In 
handling they may be readily distinguished from sound 
bulbs. 

The spores are liberated in abundance in the soil, where 
they remain alive for many years. There is no record of 
soil once smutted having become free of the smut. The 
disease may be carried to adjacent fields by insects, also 
by the means suggested under soil diseases. There is lit- 
tle or no danger of disease carriage by the seed. 

Since onion sets are immune, the effects of the smut can 
be avoided by sowing seed in soil that is free of disease and 
then transplanting into the field. With this mode of onion 
culture the only difficulty is to secure plats free from in- 
fection, and this is not often a serious one. In extreme 
cases disinfection of the soil in plats may be resorted to. 
(See soil disinfection, p. 54.) On farms once infested all 
refuse (screenings, tops of infected sets,) should be col- 
lected and burned to reduce the amount of spores. Where 
soil known to be infected is to be planted, formalin 1 
(1 pound in 25 to 33 gallons of water) should be used 
and applied with a drip attachment on a seed drill at the 
rate of 500 to 700 gallons of solution for each acre for 

1 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 131, p. 51. 



250 DISEASES OF ECONOMIC PLANTS 

onion set seeding (about one fifth to one fourth as much for 
field onions) ; or it may be applied with a sprinkler so as 
to well moisten the scattered seeds, which should then be 
covered promptly with earth. 

Ground quicklime or stone lime, better the former, ap- 
plied at the rate of 75 to 125 bushels per acre on the freshly 
prepared soil just before seeding, has been useful. If ap- 
plied by drill, harrowing will not be required ; if broadcast, 
harrowing should precede planting. 

These methods used separately or combined are suffi- 
ciently established to warrant general use on smutted soils 
devoted to onions. 

Downy mildew, blight (Peronospora schleideni Ung.). — 
Close kin to the disastrous blight of potatoes, this dis- 
ease partakes of many of its characters, particularly in the 
rapidity of its spread through an infected field. It may first 
be noted on a small area of the field in which the tips ap- 
pear as though dashed with scalding water. Often under 
favorable climatic conditions the affected areas increase 
manyfold in a single night, carrying complete destruction. 

It was first described in 1841 by Berkeley as " common 
and destructive," and has been long known to onion growers 
in this country, in Europe, and in Bermuda. In the latter 
place it was so injurious that the legislature applied to the 
mother country for investigation and aid. The first refer- 
ence to it in the United States was in 1872. It is now 
known from coast to coast. 

The blight was described fully by Thaxter in 1889, 1 again 
by Whetzel in 1904, 2 during which latter year it was par- 

1 Thaxter, R., Conn. Agr. Exp. Sta. Rpt., 1889. 

* Whetzel, H. H., N.Y. (Cornell) Agr. Exp. Sta. Bui. 218, April, 1904. 



VEGETABLE AND FIELD CROPS 



251 



ticularly destructive in New York, causing a loss of half 
the yield, or more in some instances. 

The attack in the field occurs first 
upon a few plants during warm, damp 
weather. Examined while the dew is 
still present, these plants, seen from 
considerable distance, display a pecul- 
iar violet tint especially easy to discern 
through the dewy covering. Close 
examination shows the affected part 
to be covered with a furry coating. 
On the second day these parts lose 
their green color, turn pale, or even 
yellow. On the third or fourth day 
the plant is entirely collapsed. 

The diseased spots in the field may 
each cover an area of only a few feet 
in diameter, enlarging slowly. If the 
weather favors the fungus, the disease 
may sweep rapidly across the whole 
field. Affected plants, under suitable 
weather conditions, brilliant, dry at- 
mosphere, slowly recover, putting out 
new leaves to replace the dead and 
lost. Subsequent attacks may occur 
if the weather favors the growth of 
the fungus. The injury from this dis- 
ease is through the loss of leaf surface, 
thus reducing the growing power of the plant. Usually 
little or no increase in the size of the bulb occurs after a 
severe attack. 




Fig. 112. — Onion plant 
illustrating manner of 
death of leaves affected 
with downy mildew. 
After Whetzel. 



252 DISEASES OF ECONOMIC PLANTS 

To prevent the spread of the disease, and to lessen the 
danger from subsequent attacks, a spray of Bordeaux 
mixture, 5-5-50, applied as soon as the disease is noticed, 
is needed. Careful supervision and spraying to check 
renewed attacks of the fungus, particularly if the weather 
continues to favor the fungus, should not be neglected. 
New growth should also be protected by the use of Bor- 
deaux mixture. 

If subject to this disease in previous years, it is well to 
spray before the disease appears; also throughout the 
season, reaching all sides of the leaf with the fine spray 
and using high pressure to make the mixture stick to the 
smooth onion leaves. 

Wet lands are more subject to this disease and should be 
avoided if possible. It is recommended to rake and burn 
the dead tops, to destroy the infective spores within them, 
and to practice crop rotation. 

Vermiculariose (Vermicularia circinans Berk.). — The 
outer scales of the bulb after harvest often show black 
growths of peculiar and striking character. They consist 
of central black dots or very small rings, around which 
from one to several larger rings are arranged concentric- 
ally. Under moist conditions these markings enlarge 
rapidly by the production of more rings or wavy lines, 
or, under some circumstances, the whole area may be 
overgrown with black. Later the disease may extend 
through the outer bulb scale and into the next and suc- 
ceeding layers to considerable depth, causing a dry, black 
rot. 

The black spots and rings are due to the pycnidia of a 
fungus, each pycnidium closely studded with numerous 



VEGETABLE AND FIELD CROPS 253 

stiff black spines or hairs. Sometimes flattened black 
sclerotia accompany these growths. 

While the disease is not conspicuous before harvest, it 
is really present in incipient stage upon the bulbs in the 
field and continues to develop rapidly under storage con- 
ditions. Here it may pass to new bulbs by contact or by 
air currents. These dangers are much augmented by a 
moist atmosphere. While the growth is not retarded 
appreciably by this disease, the value of the onion is often 
much reduced by the disfiguring growth, and the loss from 
rot induced by it is also considerable. 

Onions before they are placed in storage should be well 
dried. Storage bins with good ventilation, so arranged 
as to prevent all heating or sweating of the bulbs, should 
be provided. No infected bulbs should be stored, since 
they will carry infection to the sound bulbs. Bins that 
are known to be infected, i.e., which held infected onions 
in any preceding year, should be disinfected by a thorough 
spraying with Bordeaux mixture or plain bluestone so- 
lution. 

Soft rot (Bacillus 1 sp.). — This soft rot appeared in New 
York in 1898. In many cases one third to one half of the 
crop was destroyed, and the sale of the balance injured 
because the news of the presence of the rot had reached 
the buyers. 

Where the rot starts at the tip of the bulb, the onion may 
appear sound, but pressure at the top or sectioning with 
a knife reveals the rot within. Frequently a single leaf 
scale is rotten entirely around the onion, which is other- 

1 Stewart, F. C, N.Y. (Geneva) Agr. Exp. Sta. Bui. 164, December 
1899. 



254 



DISEASES OF ECONOMIC PLANTS 



wise sound: or again several scales may be rotted. If the 
outer scale is rotted, the bulbs are designated as " slippery 
onions " by the growers. The rot does not spread from 
scale to scale within the bulb. In storage it does not 
progress rapidly in dry onions, but wet onions do rot 





Fig. 113. — Onion affected with soft rot; longitudinal and cross section. After 

Stewart. 



rapidly. The only suggestion toward control is to keep 
the onions dry in storage. 

Black mold (Macrosporium parasiticum Thuem.). — Fre- 
quently onion leaves which have been injured by some 
cause, also old stems or seed stalks, assume a velvety, black 
coating which often covers them entirely. This condition 
follows only upon previous injury, weakening, or death, 
from some other primary cause, chiefly as a sequel of the 
downy mildew. Though not a primary disease its pres- 
ence extends the injury started by other causes, breaks 



VEGETABLE AND FIELD CROPS 255 

stalks which would otherwise stand, and aids in rapid 
rotting.. 

Treatment against other diseases and maintenance of 
the plants in full vigor is of most service in this case. 

Black mold (Macrosporiwn Porri Ell.). — This black mold 
much resembles the last, but its spots are somewhat more 
pale and usually more definite, less diffuse, and less liable 
to induce rotting. It does not habitually associate with 
the downy mildew, and is more truly saprophytic than the 
black mold above mentioned. While usually upon the seed 
onions, it is sometimes found upon market onions. 

The treatment suggested above applies here. 

Damping off. See p. 60. 

PARSLEY 

Sclerotiniose, drop, crown rot (Sclerotinia Libertiana 
Fckl.). — Parsley in the greenhouse is sometimes affected 
with this disease, which is identical with the lettuce drop. 

PARSNIP 

Leaf spot (Cercospora Apii Fr.). — This is the most 
common disease of the parsnip, occurring as a leaf spot 
similar to that upon celery, and caused by a very similar 
fungus. 

PEA 

Spot, ascochytose (Ascochyta Pisi Lib.). — Spotting of 
the pea leaves and pods has been known to farmers for 
many years. It is most conspicuous upon the pods as 
circular, somewhat sunken spots, 3-6 mm. in diameter, 
which are dark bordered, pale in the centers, or, when 




Fig. 114. — Pea leaves showing spots due to the blight (ascochytose). 
After van Hook. 






VEGETABLE AND FIELD CROPS 



257 



mature, somewhat pink. In these spots pycnidia are 
visible in abundance, and under favorable conditions the 
spore masses may be seen 
issuing from them, even with 
the naked eye. Upon the 
leaves similar oval spots, 3-10 
mm. in diameter, with the 
pycnidia usually in concentric 
circles, are very abundant. 
The lower older leaves are 
affected first, resulting in 
their death. The younger 
leaves die later. Stems are 
subject to the same attack 
— first near the ground, later 
upon all parts; the spots 
often penetrating through the 
woody part, thus causing wilt- 
ing and death of the parts 
beyond. The stem attack is 
the most serious form, since 
it directly causes death to a 
large part of the plant. This 

is especially true if the disease Fig. 115. — Pods of French June field 

be followed by dry weather. ^ ^ d by ascoc ^ tose - After 

All forms of the disease 
tend to decrease the yield just in proportion to their prev- 
alence. Plants not killed before flowering may develop 
pods, though of lessened yield. 

Disease upon the pod may penetrate completely through 
it and appear upon the opposite side, or more frequently 




258 DISEASES OF ECONOMIC PLANTS 

it may grow into the seed within the pod. Seeds badly 
diseased in this manner adhere to the pod; if less badly 
diseased, they thresh out, are shrunken, and show, accord- 
ing to the color of the variety, more or less discolored spots. 
Often seeds are diseased, and yet so slightly disfigured as 
to escape observation. 

Trial has demonstrated that of badly infested seeds only 
6 per cent are capable of germination, and that even when 
they do germinate, the resulting plants seldom reach ma- 
turity. On young plants the disease often assumes the 
character of damping off. 

Selby 1 makes the following notes as to varietal resist- 
ance to this disease. 

Very badly affected: French June, Market Garden, 
Dwarf Telephone, American Wonder. 

Badly affected : Admiral, Telephone, Prosperity, Advancer. 

Slightly affected : Alaska. 

Aside from the pea this disease is said to attack alfalfa, 
bean, and hairy vetch. The disease was a grave menace 
in Europe in 1894, in Canada in 1903, in Ohio in 1904. 
In New York, in 1906, from 50 to 80 per cent of the crop 
was injured. 

Two years' rotation in nonsusceptible crops lessens the 
evil very much. Diseased seed should be avoided. 

Powdery mildew (Erysiphe polygoni DC). — This mildew 
presents the usual character of the powdery mildew as 
described for grape — a whitish, powdery coating upon the 
plant surfaces. It develops most conspicuously late in 
the season, and sometimes becomes so injurious that the 
plants do not mature seed, though it is not usually very 

1 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 173. 



VEGETABLE AND FIELD CROPS 259 

destructive. Twenty per cent injury has been reported 
from Ohio; 33 per cent from some parts of Nebraska. 
The fungus hibernates in seed derived from affected pods. 
Such seed should not be used for planting. Liver of 
sulphur or Bordeaux mixture is effective in the field. 

Damping off. See p. 60. 

Rust. See bean. 

Leaf spot, septoriose (Septoria Pisi Westd.). — This 
disease cannot well be distinguished from ascochytose 
without the use of the microscope. 

Pleosporose (Pleospora Pisi (Sow.) Fckl.). — Frequently 
moldy black spots are noted upon pea pods, leaves, or other 
parts. This condition is chiefly a secondary disease follow- 
ing injury by some other disease. 

Rhizoctoniose. See p. 61. 

PEANUT 

Leaf spot, cercosporose (Cercospora per sonata (B. & C.) 
Ell.). — This leaf spot is circular in outline, indefinitely 
bordered, black to brown in the center and grading to 
green on its outer edge. The lower leaves are first 
affected and suffer most; later the disease spreads to 
upper leaves. The leaves begin to fall soon after they 
spot, and in many cases the death of the plant results. It 
is often a pest. 

The fungus causing this disease was first collected in 
Carolina and Alabama by Ravenel. 

PEPPER 

Southern blight, wilt (SclerotiumRolfsii Sacc. in litt.). — 
The blight shows itself first as a slight drooping of the 



260 DISEASES OF ECONOMIC PLANTS 

leaf tips by day, followed by night recovery. The wilting 
becomes more pronounced on succeeding days until in the 
third or fourth day the leaves wilt permanently, lose color, 




Fig. 116. — Peanut leaf spot cercosporose. Original. 



dry, and soon fall. These stages may succeed each other 
so rapidly as to appear almost simultaneous. The roots 
appear normal ; but on the stem near the ground are found 
shrunken, discolored areas in the bark, often extending 
considerable of the way around the stem. Later the roots 
may rot from secondary causes. 



VEGETABLE AND FIELD CROPS 



261 



Upon the diseased spots are fine mycelial strands, es- 
pecially abundant under humid conditions. Soon these 
strands aggregate into tufts which round off, become hard 




Fig. 117. — Pepper plant showing wilt (sclerotiose) . After Fulton. 



and smooth, and change from white to yellow, and finally 
to dark brown. These bodies, the sclerotia, are about 
as large as a mustard seed. Attacks usually begin when 
the pods are forming and continue through the season. 



262 



DISEASES OF ECONOMIC PLANTS 



This disease was first described by Rolfs 1 from Florida 
and has since been found in many Southern States upon a 
wide range of plants. 

The application of a clear, preventive fungicide, such as 

ammoniacal copper 
carbonate, to the 
ground at the base 
of the plant, and 
where any part 
touches the ground, 
so that it can soak 
into the ground near 
by and cover the 
stem itself, has 
proved beneficial. 
The first application 
should be made at 
the earliest sign of 
the blight, or still 
better, in anticipa- 
tion of it, and should 
be followed by other 
applications at in- 
tervals of two to 
three weeks. Bor- 
deaux mixture is not suitable, since the effective part of it 
is filtered out by the soil. 

Anthracnose (Glmosporium piperatum Ell. & Ev.). — ■ 
Soft, circular, pale, sunken spots upon the fruit accom- 
panied by small, ruptured spots in the skin, through which 
the. pink spore masses protrude, indicate this disease. 

i Rolfs, P. H., Ma. Agr. Exp. Sta. Rpt., 1893. 




Fig. 



118. — Pepper plant showing fungus, Sclero- 
tium Rolfsii Sacc. After Fulton. 



VEGETABLE AND FIELD CROPS 263 

Anthracnose, colletotrichose (Colletotrichum nigrum 
Ell. & Halst.). — This disease resembles the last except that 
the centers of the soft spots change to a decided black as 
they age. 

Leaf spot, phyllostictose (Phyllosticta sp.). — Small, cir- 
cular, leaf spots of ashen color bearing pycnidia indicate 
phyllostictose. 

Macrosporiose (Macrosporium sp.) . — This malady renders 
the fruit moldy and black, particularly at the blossom 
end. It is one of the most destructive of pepper diseases. 

POTATO 

Late blight, downy mildew (Phytophthora infestans (Mont.) 
DeBy.). — In the year 1889 Lamson-Scribner, 1 writing of 
this, the most serious potato disease, said, " It prevails in 
all potato countries of the world, and causes more damage 
to the potato than all other injuries combined." It is 
possible that all that Scribner regarded as blight would 
not to-day be included under the disease at present under 
discussion; still the disease holds its place among the worst 
of plant diseases of the world. 

It is estimated that in New York State alone the blight 
has caused a loss of $10,000,000 in one year, and the annual 
loss in the United States is placed at $36,000,000. 2 The 
loss reported in one year from Ohio was $2,000,000 ; from 
Wisconsin $5,000,000. The blight is supposed to have 
originated in South America and to have been brought to 
this country about 1840. 

The disease may appear on any part of the leaf, but the 

1 Lamson-Scribner, F., Tenn. Agr. Exp. Sta. Bui. 2, 2, April, 1889. 
* Orton, W. A., U.S. Dept. Agr. Yearbook, 1908, p. 453. 



264 



DISEASES OF ECONOMIC PLANTS 



spots generally show first near the tip or margin, probably 
because surface water remains longer on these parts. The 
diseased area soon dies and blackens. It may temporarily 
dry out and curl up if the progress of the fungus is 
checked by drought, or it may, in rainy weather, rap- 




Fig. 119. — Potato late blight. Rows at left sprayed with Bordeaux 
mixture and Paris green ; rows at right received Paris green only. 
Original. 



idly proceed to transform the entire foliage into a moist, 
putrid mass. In the earlier stage the blackened part is 
bordered by a narrow region of light green, characterized 
by a slightly watery, flaccid appearance. Under con- 
ditions of especially humid atmosphere a fine, white down 
may be seen upon the more recently invaded parts. This 
affection of the leaves is accompanied by an offensive odor 



VEGETABLE AND FIELD CROPS 265 

discernible at considerable distance from the field. The 
disease usually soon shows on the stems also, which in turn 
blacken and die. 

On the tuber the surface shows slightly depressed dark- 
colored areas, while internally the normal white color 
changes to dirty brown. If the soil is dry, dry rot results ; 
if wet, the tubers decay as wet, slimy, ill-smelling masses. 
In storage the disease continues, and the loss sustained in 
the field may be greatly augmented. 

This blight is closely dependent upon weather conditions 
of heat and moisture. A daily mean of 72°-74° F. accom- 
panied by moist weather is best for its spread. A daily 
mean temperature above 77° F. for a- few days retards its 
development. 

Although the conspicuous signs above noted first attract 
the attention of the general observer, the disease really 
commences as soon as the sprouts appear upon some of 
the young plants grown from infected seed. Such shoots 
remain dwarfed, assume a reddish brown color, and when 
proper weather conditions obtain, furnish the spores to 
start the general epidemic. 

Marked difference in resistance exists between different 
varieties. Thus Woods of Maine found that the Rust- 
proof showed the highest resistance, about 1 per cent of 
disease, while no other varieties tried gave less than 30 per 
cent of disease. Of the standard crop varieties the follow- 
ing are reputed to possess some degree of resistance : Car- 
men No. 3, Sir Walter Raleigh, Rural New Yorker No. 2, 
Rural Blush, Green Mountain, State of Maine, Delaware, 
Enormous, and White Beauty. 1 

1 Jones, L. R., U.S. Dept. Agr. Bur. Plant Indus. Bui. 87. 



266 DISEASES OF ECONOMIC PLANTS 

Field trials by William Stuart 1 have shown that certain 
German and English varieties are more highly resistant 
than the American varieties. It is a hopeful sign, there- 
fore, that American potato breeders are now giving atten- 
tion to disease resistance and that new varieties of better 
value in this respect may be expected in the future. 

Potatoes free from the disease should be used for seed. 
Diseased potatoes may be recognized by their reddish 
brown surface color, which extends toward the center of 
the potato; also by the slight shrinking of the surface in 
such parts, or by the black spotting described above. 

The crop should also be sprayed as recommended under 
the general heading, p. 281. Though the disease may 
not develop every year in severe epidemic form, spraying 
is necessary each year as a preventive measure. Since the 
blight develops so rapidly, it is quite impracticable -to wait 
for signs of the disease before spraying is begun. Moreover, 
experiments extending over several years have shown that 
even in years when the blight does not become epidemic, 
sufficient benefit is derived from spraying to warrant its 
adoption. 

The Geneva Experiment Station says : 2 " Judging from 
the experiments thus far made, it appears that spraying 
for blight is an operation which no potato grower in New 
York can afford to neglect. Forty-eight farmers' business 
experiments made during the past four years show an 
average net profit of $20.51 per acre due to spraying. 

1 Jones, L. R., and Morse, W. J., Vt. Agr. Exp. Sta. Rpt. 16, p. 163, 
1902-1903. 

2 Stewart, F. C, and others, N.Y. (Geneva) Agr. Exp. Sta. Bui. 290, p. 
240, June, 1907. 



VEGETABLE AND FIELD CROPS 



267 



Commence spraying with Bordeaux when plants are 
6 to 8 inches high and repeat at intervals of 10 to 14 days 
throughout the season, making, in all, five or six applica- 
tions. When bugs or flea beetles are numerous, add Paris 
green or other poison. In case the tops have blighted, the 




Fig. 120. — Potato scab, a, natural ; b, produced by inocula- 
tion forming monogram R. T. After Conn. Agr. Exp. Sta. 



danger of tuber infection and consequent rot is lessened 
by delaying the harvest of the tubers until at least a week 
or ten days after the death of the foliage. 1 

Scab (Oospora scabies Thaxt.). — Potato scab prevails 
in Europe, Africa, New Zealand, in all parts of the United 
States, and probably everywhere the potato is grown. 
Though practically all American potato scab may be 
classed as one disease, there is some evidence that there 
is more than one form of disease which passes under this 



1 Jones, L. R., and Morse, W. J., Vt. Agr. Exp. Sta. Rpt. 16, p. 163, 
1902-1903. 



268 DISEASES OF ECONOMIC PLANTS 

name in Europe. 1 It was first attributed to its proper 
cause by Dr. Thaxter 2 in 1890. 

The scab is recognized by all potato growers as a char- 
acteristic rough pitting of the tubers. If these are attacked 
when quite young, the scabs are deep ; if the attack is later, 
they are more shallow. In very severe cases the tuber is 
furrowed or cracked. 

The scab at first appears as a minute reddish or brownish 
surface spot, often when the potato is very young. It 
extends outward, deepens in color, and is attended with 
the development of an irregular corky incrustation. 

The disease is often prevalent to such extent as to pro- 
hibit successful potato culture. The chief loss comes from 
depreciation in sale value, though there is also loss in yield. 
Estimates show that from 5 to 75 per cent of the potato 
crop is unsalable on account of scab. The loss in one 
county alone in California is placed at $300,000 yearly. 

Scab is most prevalent in alkaline soils and is favored by 
moisture. Wood ashes, potash, soda, stable manure, lime 
etc., increasing alkalinity, favor the growth of the fungus, 
and cause increase in the amount of scab in soil already 
infected. Materials which tend to decrease scab are com- 
mercial fertilizers, potash salts (except carbonate), land 
plaster, and ammonium sulphate. Rotation of crops tends 
to diminish the amount of scab, provided other susceptible 
crops, as beets, turnips, cabbages, etc., are avoided. A 
three-year rotation without a susceptible crop largely 
reduces it, though after five or even ten years the disease is 
not entirely exterminated. During rotation any practice 

1 Jones, L. R., U.S. Dept. Agr. Bur. Plant Indus. Bui. 87. 

2 Thaxter, R., Ct. State Agr. Exp. Sta. Rpt. 14, pp. 81-95. 



VEGETABLE AND FIELD CROPS 269 

that increases the acidity of the soil aids in reducing 
the scab. Thus plowing under green crops is a favorable 
practice. 

In general it may be said that scabby seed potatoes in any 
soil will produce a scabby crop, but the amount of scab is 
determined somewhat by the soil condition. Seed potatoes 
free from scab, in a soil free from scab, will raise a crop free 
from scab. Seed potatoes free from scab will not produce 
a healthy crop if grown in an infected soil. 

There is much difference in varietal resistance to scab. 
The more resistant varieties should be used on soil at all 
scab infested. Cambridge Russett, Carmen No. 3, Ameri- 
can Giant, Sir Walter Raleigh, Irish Cobbler, Scab Proof, 
and Aurora are recommended by the Maryland Station as 
possessing some scab resistance. 1 

Two conditions arise . requiring different cultural 
methods : — 

1. The management of clean soils. 

2. The management of soils already infected. 

If the land is free from infection, great care should ,be 
exercised to avoid introduction of the scab fungus by any of 
the general means suggested under soil disease. In par- 
ticular, infection may occur by the use of scabby seed, or 
through the use of manure which has been infected by feed- 
ing uncooked scabby potatoes to stock. If seed must 
be planted that cannot safely be regarded as free from 
scab, and no seed from an unknown source can be so 
regarded, it should be disinfected to free it of all scab 
germs. 

To disinfect potato seed the most effective method is by 

1 Norton, J. B. S., Md. Agr. Exp. Sta. Bui. 108, p. 67, April, 1906. 



270 DISEASES OF ECONOMIC PLANTS 

the use of formaldehyde gas x liberated by mixing the com- 
mercial solution with potassium permanganate. This 
method is adapted to the disinfection of large quantities of 
potatoes in a short time. To use it, an air-tight shed should 
be constructed of sufficient size to hold whatever quantity 
it may be desired to treat at one time. This may be made of 
rough lumber lined with building paper and provided with 
a tight door. The potatoes may be treated in sacks, but 
these sacks should be so piled as to permit free circulation 
of air all around them. It is suggested that they be piled 
in tiers with two 2-by-4-inch scantlings between each layer 
of sacks. Space should be left in the center of the building 
for placing the charge of formaldehyde, which should be 
set off in shallow vessels, such as galvanized washtubs. For 
each 1000 cubic feet 23 ounces of potassium permanganate 
and 3 pints of formaldehyde should be allowed. After the 
potatoes are properly stacked and everything is made ready, 
the permanganate should be spread in a thin layer on the 
bottom of the pan, the required quantity of formaldehyde 
poured in, stirred quickly, .and the building vacated. The 
building should then be kept tightly closed for twenty-four 
hours, when it may be opened and the potatoes taken out. 
The precaution should be taken not to pile any potatoes 
directly over the pans or within three feet laterally, since 
the gas there might be strong enough to injure the potatoes 
and destroy their germinating power. The formaldehyde 
works best in a humid atmosphere. It is therefore advised 
that the floor of the shed be dampened before the treatment 
is made. The potatoes, however, should not be moist, 

1 Jones, L. R., and Edson, A. W., Vt. Agr. Exp. Sta. Rpt. 14, 1900-1901, 
and Morse, W. J., Me. Agr. Exp. Sta. Bui. 141, p. 89, March, 1907, 



VEGETABLE AND FIELD CHOPS 271 

since the disinfection is more thorough if the surfaces are 
dry. 

The cost of materials for treatment need not amount to 
over one cent a sack. For example, a shed 12 by 24 feet and 
7 feet high contains 2016 cubic feet and would require 3 
pounds of potassium permanganate, costing 60 cents, and 
6 pints of formaldehyde, costing $1.20; total, $1.80. Two 
hundred sacks can easily be treated at one time in such a 
shed. 

Small quantities of potatoes may be disinfected by soak- 
ing in a solution of 1 pint of formaldehyde to 30 gallons 
of water for 2 hours, or 1^ hours in corrosive sublimate 
solution, 2 ounces to 2 gallons of hot water, then diluted to 15 
gallons. Either the gas or the solution treatment may be 
applied some time previous to planting, provided the pota- 
toes are not exposed to reinfection by being put into recep- 
tacles, bags, buckets, etc., that have previously held scabby 
potatoes. The treatment should be made before the pota- 
toes are cut for planting. 

No system of soil treatment has proved reliable in the 
management of infected land. Long rotation avoiding 
susceptible root crops should be practiced. The use of 
fertilizing materials which favor the fungus should be avoided 
and resistant varieties should be planted. The turning 
under of a green crop, e.g., rye, may gradually decrease the 
scab tendency. 

Rosette, stem rot, little potato (Corticium vagum B. & C. 
var. solani Burt.). — Though particularly prevalent in the 
Middle West and Rocky Mountain states this pest is known 
generally in the east from Connecticut south. 

Aerial potatoes, potatoes borne upon the parts of the stem 



272 



DISEASES OF ECONOMIC PLANTS 



above ground, are 
conspicuous in 
this disease. 
Other characters 
are rotting of the 
stem, the rosette 
development of 
the tops, and a 
scabby growth 
upon the tubers. 
Infected potatoes 
in storage may 
give way to a wet 
rot. In Florida 
in 1904 scarcely a 
lot of seed pota- 
toes free of this 
disease could be 
found, and the 
hibernating con- 
dition of the fun- 
gus was evident 
in 60 per cent of 
the seed tubers in 
some instances. 1 
Such infected 
tubers are largely 

responsible for the contamination of new soil. 

Diseased seed tubers may be recognized by the superficial, 

irregularly shaped, elevated, dark brown patches of fungous 

1 Hume, H. H., Fla. Agr. Exp. Sta. Bui. 75, p. 188, August, 1904. 





a m 


' t j 


^tL 1 -'■■- 


• 




<C«^a 


W0 




\\| 


■ 1 im 
m. f'M 

Wk 'Jr 

f 


:; 'j 




SP5w 





Fig. 121. — Little potatoes and aerial potatoes. 
After Rolfs. 



VEGETABLE AND FIELD CROPS 273 

threads (sclerotia), varying in size from a pinhead to a grain 
of wheat. They are seen clearly only when the tuber is wet. 

Soon after planting the young sprouts are attacked by 
this waiting fungus. Black spots appear near the surface of 
the ground, destroying the bark and often girdling the stem. 
A dark network of fungous threads is sometimes seen upon 
the subterranean parts. This advances above ground and 
develops a gray spore-bearing layer about the green stem, 
often extending upward several centimeters, causing the 
young shoots to wilt, droop, and die. Often a loss of one 
fourth to one third of the plants follows. Those stems 
which survive this early attack, but which are attacked later, 
show the aerial tubers mentioned above and produce a few 
underground tubers ; and these small and unsalable. Such 
tops may develop peculiar twisted leaves with prominent 
veins and bear their leaves in a crowded manner that enables 
their easy recognition, even from some distance. If these 
plants be examined closely, the injury caused by the fungus 
will frequently be found as a wound often 2-3 cm. long 
upon the stem at or near the surface of the ground. 

In some of these symptoms this disease closely resembles 
the bacterial malady known as " blackleg," which is de- 
scribed upon a later page. Fortunately the remedial meas- 
ures are similar. 

Only clean seed should be used. If there is any doubt as 
to freedom of the seed from the disease, it should be treated 
as is recommended for potato scab. Liming the soil, clean 
culture methods, and crop rotation are preventive. Infected 
refuse should be destroyed by fire. Soil badly infested 
should not be planted in potatoes. In general the remarks 
made under soil diseases apply here. 



274 



DISEASES OF ECONOMIC PLANTS 



While this disease as caused by Rhizoctonia has long been 
known in Europe, especially in Germany, no record of it 







Fig. 122. — Potato attacked by Corticium. After Rolfs. 



was made in America until 1891. Since that date it has 
been noted upon many hosts in many states. See p. 61. 



VEGETABLE AND FIELD CROPS 275 

Early blight (Alternaria solani (E. & M.) J. & G.). — 
This is one of the very serious potato diseases that pre- 
vail throughout the country. In 1906 the loss in Wiscon- 
sin was placed at about 5,000,000 bushels, and a 50 per cent 
loss was reported from Wyoming. 

The grayish brown leaf spots', which are brittle, irregularly 
circular, and are concentrically marked, appear about the 
time the tubers begin to form. The coalescence of the spots 
involves large areas of leaf tissue and results in browned, 
withered leaves, the stems remaining green. The effect 
is often so complete as to lead the grower to think the vines 
have died a natural death. The progress of the disease is slow, 
covering three or four weeks before all the leaves are dead. 
The loss of efficient leaf tissue so diminishes the vigor of the 
plant that the yield is largely reduced. Though the tubers 
are not directly attacked and never rot from this disease, 
their growth is usually stopped at the attack of the disease. 
This is a disease characteristic of dry soils and seasons, and 
is liable to be associated with tip-burn. 

The general spraying (p. 281) will hold this blight in check. 

Wilt, fusariose (Fusarium oxysporum Schlecht.). — This 
wilt is definitely known in Michigan, Virginia, North 
Carolina, Ohio, Kansas, Nebraska, District of Columbia, 
New York, Florida, California, Colorado, Wisconsin, Oregon, 
Washington, Massachusetts, Iowa, West Virginia, and Ver- 
mont, and is probably identical with a very destructive 
potato disease of England, Germany, France, and Belgium. 

When the plants are about a foot high, or in mild cases a 
little later, the first trace of the wilt is noticeable. 1 The 

1 Smith, E. F., and Swingle, D. B„ U.S. Dept. Agr. Bur. Plant Indus. 
Bui. 55, February, 1904. 



276 DISEASES OF ECONOMIC PLANTS 

leaves, which are usually light colored, assume a dull, un- 
healthy appearance, with rolling or curling of the margins. 
Progressive disease gradually causes the top to fall, and 
gives a general effect of premature ripening. When the 
diseased plants are pulled up, the roots are found to 
be partly dead, quite brittle, and frequently bearing a 
white or pink mold. When the underground portion of 
the stem is cut across, a pronounced brown discoloration is 
visible. This brown stain is also found in the branches 
leading to the tubers, and a thin slice across the stem end of 
the tuber will often reveal its presence there as well. 

The loss caused amounts to millions of dollars annually, 
due: (1) to deficient germination; (2) to early ripening and 
thus to diminished yield; (3) to dry rot in storage. 

When the potatoes are dug, there is rarely any external 
evidence of the disease on them. The major portion of the 
crop produced from wilted plants is nevertheless infected. 
If these potatoes are stored in a cold place, but little change 
occurs; but when infected potatoes are kept in a heated 
room or left outdoors in a warm climate, a dry rot soon 
develops. 

Beginning at the stem end the tuber shrivels, the inside 
becoming brown and light in weight. Occasionally bacteria 
cause a secondary soft rot, which proceeds more rapidly. 
An early form of this dry end rot is frequently met with 
shortly after the potaoes are harvested. Potatoes thus af- 
fected are known to buyers as " jelly ends." 

The presence of this disease can be detected in otherwise 
normal tubers only by making a thin slice across the stem 
end and searching for the brown discoloration. Such pota- 
toes are not desirable for seed, but are not objectionable for 



VEGETABLE AND FIELD CROPS 211 

cooking, provided they are consumed promptly or kept in 
cold storage. 

This wilt is closely related to the watermelon and cotton 
wilt. Soils which have once borne a sick crop are infected 
and will infect future crops. The general means by which 
a field may become infected have been discussed on page 65. 
In addition to these means of infection, the potato wilt is 
often carried to new fields by infected " seed." 

For this reason all seed introduced from other fields 
should be carefully inspected to guard against such infection. 
It is a matter of record that this disease was largely intro- 
duced into California from Oregon by means of infected 
tubers. A little care a few years ago would have accom- 
plished what seems now to be impossible, the prevention of 
the disease in that region. Residents of other regions still 
uninfected should profit by this example and exercise such 
precaution as to avoid a similar fate. The disease may pass 
to the manure by feeding infected potatoes to stock, and 
this manure may lead to the infection of new fields. 

Crop rotation will partially restore infected fields to health. 
Collecting and burning of the tops after digging will diminish 
the amount of the fungus and add to the benefit of rotation. 

If diseased potatoes must be stored for any length of time, 
all that are badly diseased should be rejected, and the re- 
mainder kept as cool as possible without freezing them. It 
is best to sell or consume such tubers at once. 

Wilt, bacillose (Bacillus solanacearum E. F. Smith). — 
This wilt, chiefly prevalent from Maryland southward, 
reported also from Indiana, Nebraska, and Iowa, is identi- 
cal with that of eggplant, tobacco, and tomato, and is to a 
large extent transmitted to the plants by insects. 



278 DISEASES OF ECONOMIC PLANTS 

The leaves wilt, and dry up ; the stems and tubers show 
yellowing and blackening in the veins, and the tubers give 
way in a soft rot. Squeezing the diseased tubers causes ex- 
udation of creamy drops from the diseased veins. 

Tubers from diseased vines rot rapidly and should not 
be stored if it can be avoided. If stored, they should be 
kept at as low a temperature as possible. It is unwise to 
plant potatoes in land which has shown this disease upon 
any of its hosts without a long intervening rotation. The 
precautions suggested under soil diseases, use of clean seed 
and special attention to insect control, are preventive meas- 
ures. 

Cercosporose, leaf blotch (Cercospora concors (Casp.) 
Sacc). — Cercosporose of the potato has been known in 
Europe since 1854, but was not known in the United States 
until 1902, when it was found in Vermont by L. R. Jones. 
Cercosporose appears when the plants begin to blossom. 
The lower leaves show obscurely defined pale spots, 3-5 mm. 
in diameter, sometimes blending to form larger areas. 
A pale gray or violet fungus becomes conspicuous upon the 
lower surface. As the disease progresses the spots encroach 
upon the upper leaves. The affected spots sometimes die, 
much resembling the alternariose spot, but more often the 
entire leaf slowly turns yellow and dies. 

The damage, especially to late potatoes, is considerable, 
reducing the yield one fourth or more. In Europe the dis- 
ease is troublesome, and its spread in this country may be 
anticipated. 

The following varietal resistance was noted by Jones and 
Pomeroy : 1 — 

1 Jones, L. R., Vt. Agr. Exp. Sta. Rpt. 19, 255. 






.VEGETABLE AND FIELD CHOPS 279 

Badly affected: Early Ohio, Early Rose, Holborn or 
Abundance, Swiss, Snowflake. Slightly affected : Blight 
Proof, Rural New Yorker No. 2. Not affected : Delaware, 
Rural Blush. 

Rot (Rhizopus nigricans Ehrbg.). — Orton 1 has described 
a soft rot of potato native to the peat lands of California. It 
is characterized by dull brown discoloration of the skin and 
light brown or buff coloring of the flesh, accompanied by 
softening. Upon pressure a clear brown liquid without 
disagreeable odor exudes. 

The disease spreads rapidly in warm weather, and entire 
shipments may decay en route to market. It gives no 
trouble after frost. To prevent infection the skin should 
not be broken in handling, and all infected refuse should 
be destroyed by fire. 

Tipburn. — The leaves die at the tips and margins, 
blacken, roll up, and break off. The disease is widespread 
in the northeastern United States, especially in dry, hot 
summer weather. 

It is not due to parasites. 2 

Blackleg, bacillose (Bacillus phytophthorus Appel.). — ■ 
Much confusion has arisen concerning the identity of black- 
leg, since in many instances the mere occurrence of a black 
region upon the stem near the ground line has led to the use 
of the term. It is thus probable that in the literature of 
potato maladies several distinct diseases have been con- 
fused with the " blackleg." 

A distinct, definite, and serious disease has, however, been 
known for several years under this name in Europe and 

1 Orton, W. A., U.S. Dept. Agr. Bur. Plant Indus. Circ. 23, January 
23, 1909. 2 Jones, L. R., Vt. Agr. Exp. Sta. Bui. 72, 1899. 



280 



DISEASES OF ECONOMIC PLANTS 



England, and thorough study by Appel in 1903 led him to 
attribute it to the bacillus above named. American studies 




Fig. 123. —Potato black leg. Original. 



render it probable that this same disease is present in this 
country, but to just what extent is uncertain because of the 



VEGETABLE AND FIELD CROPS 281 

confusion in diagnosis referred to above. L. R. Jones, 1 who 
studied blackleg in the field in Germany and England and 
what appeared to be the same disease in Vermont, described 
it essentially as follows : The earliest conspicuous symptom 
was that the diseased plants were slightly below normal 
size, of a paler or yellowish green color, the lateral branches 
and petioles becoming more erect and the leaf blades curv- 
ing upward, giving the entire plant a narrowed aspect. 
The lower leaves in the meantime have possibly shriveled 
and died. The stem was more or less browned or blackened 
from near the surface of the soil downward. In extreme 
cases the discoloration was visible 2-3 cm. above the 
soil. The tissues of the discolored part died, and the softer 
parts decayed. Usually the seed tuber also was rotted. 
Rot of the resultant crop of tubers has been reported from 
Germany, but was not observed in Vermont. 

A disease nearly related to this has been described by Har- 
rison as due to Bacillus solanisaprus. 

As yet there is little definite knowledge concerning means 
of distribution or prophylaxis. Until more definite knowl- 
edge obtains it is well to avoid badly diseased localities 
and seed potatoes from diseased regions and to give heed 
to the general suggestions under soil diseases. 

Potato Spraying 

The spraying of potatoes, as with other crops, should not 

be directed or planned to meet merely one of the diseases, 

but rather to give the plant the best possible protection 

against all of its enemies. The chief enemies to be met are 

1 Jones, L. R., Vt. Agr. Exp. Sta. Rpt. 19, p. 259, and U.S. Dept. Agr. 
Bur. Plant Indus. Bui. 87, p. 17, 1905. 



282 



DISEASES OF ECONOMIC PLANTS 



the early and late blights, and the Colorado beetle or " po- 
tato bug." 

The gains from spraying potatoes with Bordeaux mixture, 
as shown in trials at the Vermont Experimental Station, 1 
begun in 1891 by Jones and extending over seventeen 
years, are shown below: — 

Gains from the Use of Bordeaux Mixture on Late 
Potatoes 





Sprayed 


Yield per Acre 




Planted 


Sprayed 


Not 
Sprayed 


Gain per Acre 


White Star, 
May— ,1891 
May 20, 1892 
May 20, 1893 
Apr. 26, 1894 

May 20, 1895 
Polaris, 

May 15, 1896 

June 1, 1897 
White Star, 

May 10, 1898 
Average, 
3 varieties, 

May 18, 1899 

Delaware, 
May 23, 1900 
May 25, 1901 
May 15, 1902 

Green Mountain, 
May 1,1903 

Delaware, 
Mav 25, 1904 
May 15, 1905 

Green Mountain, 
May 27, 1906 
May 1,1907 


Aug. 26, Sept. 8 
July 30, Aug. 13, 25 
Aug. 1, 16, 29 
June 16, July 17, 

Aug. 30 
July 25, Aug. 13, 31 

Aug. 7, 21 

July 27, Aug. 17, 28 

July 21, Aug. 10 

July 26, Aug. 17, 
Sept. 8 

Aug. 4, 23 
July 20, Aug. 21 
Aug. 1, 20 

Aug. id 

Aug. 1, Sept. 1 
Aug. 2, 21 

Aug. 13, 22 
Julv 16, 25, Aug. 8, 
22 


3L3 bu. 
291 bu. 
338 bu. 

323 bu. 
389 bu. 

325 bu. 
151 bu. 

238 bu. 
/ 

229 bu. 

285 bu. 

170 bu. 
298 bu. 

361 bu. 

327 bu. 
382 bu. 

133 bu. 

171 bu. 


248 bu. 

99 bu. 

114 bu. 

251 bu. 
219 bu. 

257 bu. 
80 bu. 

112 bu. 

161 bu. 

225 bu. 

54 bu. 

164 bu. 

237 bu. 

193 bu. 
221 bu. 

101 bu. 

63 bu. 


65 bu. or 26% 
192 bu. or 194% 
224 bu. or 196% 

72 bu. or 29% 
170 bu. or 78% 

68 bu. or 26% 
71 bu. or 89% 

126 bu. or 112% 

68 bu. or 42% 

60 bu. or 27% 
116 bu. or 215% 
134 bu. or 82% 

124 bu. or 52% 

134 bu. or 69% 
161 bu. or 73% 

32 bu. or 32% 

108 bu. or 175% 


Average of 17 years, 


278 bu. 


165 bu. 


113 bu. or 68% 



i Jones, L. R., and Giddings, N. J., Vt. Agr. Exp. Sta. Rpt. 20, p. 
334 et seq., 1906-1907. 



VEGETABLE AND FIELD CROPS 



283 



Extensive experiments have been conducted for the past 
seven years by the New York Experiment Station. The fol- 
lowing table taken from bulletin 31 1 summarizes their results. 1 









At Geneva 


At Riverhead 


Year 


Gain per A. due 


Gain per A. due 


Gain per A. due 


Gain per A. due 




to spraying 


to spraying 


to spraying 


to spraying 




Every Two Weeks 


Three Times 


Every Two Weeks 


Three Times 




Bu. 


Bu. 


Bu. 


Bu. 


1902 . . 


123J 


98| 


45 


271 


1903 






118 


88 


56 


39i 


1904 






233 


191 


96 


56i 


1905 






119 


107 


82 


314 


1906 






63 


32 


53 


21i 


1907 






73| 


44 


31 


18 


1908 






39 


29i 


15| 


101 


Averag 


e 




110 


84 


54 


29 



Seven years of business experiments made on farms in 
order to determine the actual profits from spraying under 
farm conditions gave the following results: 2 — 









Average 
Increase 
in Yield 
per Acre 


Average 


Average 






Number 


Total 


Total 


Cost 


Average 


Year 


of Experi- 


Area 


Cost of 


per Acre 


Net Profit 




ments 


Sprayed 


Spraying 


for Each 


per Acre 








per Acre 


Spraying 








A. 


Bu. 








1903 


6 


61.2 


57 


$4.98 


$1.07 


$23.47 


1904 


14 


180 


62.2 


4.98 


.93 


24.86 


1905 


13 


160.7 


46.5 


4.25 


.98 


20.04 


1906 


15 


225.6 


42.6 


5.18 


.985 


13.89 


1907 


14 


152.75 


36.8 


5.90 


1.18 


17.07 


1908 


14 


200.25 


18.5 


4.30 


.92 


8.53 



Average increase in yield, for six years, 43.8 bushels per acre. 
Average net profit, for six years, $17.94 per acre. 

1 Stewart, F. C, and others, N.Y. (Geneva) Agr. Exp. Sta. Bui. 311, 
p. 13, January, 1909. 2 Ibid., p. 29. 



284 DISEASES OF ECONOMIC PLANTS 

In the Geneva and Riverhead experiments rows sprayed 
three times received Bordeaux mixture and Paris green 
twice and Bordeaux alone once, the dates being July 3, 17, 
and August 3. Other rows were sprayed six times, twice 
with Bordeaux mixture arid Paris green and four times with 
Bordeaux alone, the dates being July 3, 17, August 3, 18, 
and September 1, 16. Still other rows were not sprayed at 
all with Bordeaux, but were treated twice, July 3 and 20, 
with Paris green in limewater to control bugs. The Bor- 
deaux mixture contained 6 pounds of copper sulphate to each 
50 gallons of water and lime to correspond. Paris green 
was used at the rate of 1 pound to 50 gallons of mixture. 

The recommendation of the Geneva Station is : " Com- 
mence spraying when the plants are six to eight inches high 
and repeat the treatment at intervals of 10 to 14 days in 
order to keep the plants well covered with Bordeaux 
throughout the season. During epidemics of blight it may 
be necessary to spray as often as once a week. Usually 
six applications will be required. The Bordeaux should 
contain 4 pounds of copper sulphate to each 50 gallons 
in the first two sprayings, and 6 pounds to 50 gallons in 
subsequent sprayings. Whenever bugs or flea beetles are 
plentiful, add one to two pounds of Paris green or two 
quarts of arsenite of soda stock solution to the quantity 
of Bordeaux required to spray an acre. 

" Thoroughness of application is to be desired at all times, 
but is especially important when flea beetles are numerous 
or the weather favorable to blight. Using the same quan- 
tity of Bordeaux, frequent light applications are likely to 
be more effective than heavier applications made at long 
intervals." 



VEGETABLE AND FIELD CROPS 285 

" Those who wish to get along with three sprayings should 
postpone the first one until there is danger of injury from 
bugs or flea beetles, and then spray thoroughly with Bor- 
deaux and poison. The other two sprayings should like- 
wise be thorough and applied at such times as to keep the 
foliage protected as much as possible during the remainder 
of the season. Very satisfactory results may be obtained 
from three thorough sprayings." 

" A single spraying is better than none and will usually 
be profitable, but more are better." 

" Except, perhaps, on small areas, it does not pay to 
apply poison alone for bugs. When it is necessary to fight 
insects, use Bordeaux mixture and poison together." 

PUMPKIN 

Downy mildew. See cucumber. 
Powdery mildew. See squash. 

RADISH 

Club root. See cabbage. 

White rust (Albugo Candida (Pers.) Ktz.). — This white 
rust has the characters described under beet, and in addi- 
tion, upon this host, it often causes curious malformation 
of the flowers and pods, which become overgrown and dis- 
torted; often a flower is five times its normal diameter 
and is colorless. Chief damage is done to the seed crop, 
which may be quite ruined by this attack upon the flowers. 

Burning of all infected trash is the best preventive. 

Damping off (Rhizoctonia sp.). — Damping off and root 
rot of this crop have been noted in Connecticut. 

See damping off, p. 60. 



286 



DISEASES OF ECONOMIC PLANTS 



ROSELLE (Hibiscus Sabdariffa) 

Powdery mildew (Microsphcera Euphorbice B. & C). — 
This mildew of characteristic white, flower- 
like, circular patches has been noted in 
Florida. 

Flowers of sulphur have proved effective 
in preventing its spread, according to Bessey 
as cited by Fawcett. 1 



Fig. 124. — White 
rust (albugese) 
up on salsify 
leaves. After 
Heald. 



SALSIFY 

White rust (Albugo Tragopogonis (DC.) 
Gray). — White, rustlike, blisters (sori) 
upon the leaf indicate this disease. The 
sori are longer than broad, extending 
lengthwise of the leaf. In late stages of 
the disease the leaf near the sori blackens 
and withers, often tearing lengthwise. 

Bacteriose. — A soft rot of the roots, re- 
sulting in loss of green color and prostra- 
tion of the plants, is attributed to bacteria. 2 
The slimy, offensive decay usually begins 
at the lower end of the main root and 
progresses upward. See carrot soft rot. 

Rust (Puccinia Tragopogonis (Pers.) 
Cda.). — This true rust is of somewhat 
general distribution, but is not harmful. 

SPINACH 



Anthracnose (Colletotrichum Spinacece Ell. & Halst.). 

1 Fawcett, H. S., Fla. Agr. Exp. Sta. Rpt. 88. 

2 Halsted, B. D., N.J. Agr. Exp. Sta. Rpt, 11, 351, 1890. 



VEGETABLE AND FIELD CEO PS 



287 



Blotches 1 appear upon the leaves, first as small, moist, 

watery areas, associated with slight local wilting, followed 

soon by the appearance upon either side of the leaf of very 

small brown acervuli. The 

spots then change to gray and 

dry up. The disease spreads 

rapidly from plant to plant 

and is very destructive both 

under glass and in the open, 

rendering the plant unfit for 

use. 

White smut (Entyloma El- 
lisii Halst.). — The attacked 
plants are unmarketable, due 
to lack of uniform green color 
and the presence of pale 
bleached spots upon the foli- 
age. These spots are not 
definitely limited, nor does 
their tissue die as it does in 
the case of other spinach leaf 
spots. 

Black mold (Cladosporium 
macrocarpum Preuss.) . — The 
black mold develops especially 

upon old leaves, and renders the plant unsalable. The 
spots are distinguishable from all other spinach spot dis- 
eases by their irregularity, indefiniteness, and color. 

General. — To control all the above spinach diseases, it 
is well to burn diseased refuse, practice rotation, and 

1 Halsted, B. D., N.J. Agr. Exp. Sta. Bui. 70, July, 1890. 




Fig. 125. — Spinach leaf spotted by 
heterosporiose. After Reed. 



288 DISEASES OF ECONOMIC PLANTS 

employ preventive sprays when the plants are young. 
Spraying the edible leaves as the plants approach maturity 
injures the sale and is not permissible. 

Heterosporiose x (Heterosporium variabile Cke.). — This 
disease was especially injurious to spinach in eastern Vir- 
ginia during the winter of 1908-1909, and has also been 
noted in Connecticut. It appears early in January and 
continues to increase until the spinach season is over. 
Numerous leaf spots are produced, at first brown, later 
sooty, as the conidiophores and conidia of the fungus de- 
velop. The older leaves usually show more injury than 
the younger, but at times all leaves are seriously affected. 
The presence of the fungus renders the leaves unsalable, and 
much additional labor is required at harvest time to trim off 
the injured leaves. 

The disease does not seem capable of attacking healthy, 
vigorous plants, but usually follows injuries produced by 
some other agencies. In Virginia it has been found to fol- 
low the injuries produced by peronospora. Injuries pro- 
duced by cold weather, prolonged rains, insects, etc., un- 
doubtedly afford weak points where infection may begin. 

The best preventive measures, so far as known at present, 
are to follow general hygienic precautions, rake up and de- 
stroy all dead and diseased leaves, keep the injuries from 
insects and other fungi at a minimum, and rotate crops as 
much as possible. 

Downy mildew (Peronospora effusa (Grev.) Rbh.). — ■ 
Gray to slightly violet, downy spots upon the lower sur- 
faces of leaves, accompanied by pale yellow spots upon the 

1 This description was prepared at the request of the authors by H. S. 
Reed. 



VEGETABLE AND FIELD CROPS 289 

corresponding upper surfaces, indicate the downy mildew. 
The disease in its habit and damage resembles that of the 
grape, p. 166. 

Serious loss is reported from New Mexico and Virginia. 

Leaf blight, phyllostictose (Phyllosticta Chenopodii Sacc). 
— This disease affects the leaves, especially at their bases, 
producing spots which bear minute pycnidia. 

Cercosporose (Cercospora beticola Sacc). — This disease 
often ruins crops by yellowing and dwarfing the plants, 
thus rendering them worthless for market. By causing 
local leaf spots it diminishes the vigor of the plant. 

SQUASH 

Powdery mildew (Erysiphe cichoracearum DC). — This 
mildew is very.common upon the squash, forming the usual 
whitish coating upon the surface of the leaves and stems. 

Downy mildew. See cucumber. 

Wilt, bacillose. See cantaloupe. 

Anthracnose, colletotrichose. See watermelon. 

SWEET POTATO 

Soft rot (Rhizopus nigricans Ehrbg.). — The most prom- 
inent soft rot of the sweet potato, the only one that is 
commonly met, may be recognized by the soft, wrinkled 
condition of the potato, its sweetish odor, and usually 
by the presence of a white, later black, growth of mold, 
appearing through the skin of the rotten portion at points 
of rupture. 

The decay most often begins at one end and passes 
rapidly through the root, but it may start at a wound upon 
any part of the potato. It progresses with such rapidity 



290 



DISEASES OF ECONOMIC PLANTS 



that the whole potato may give way in a few days after 
infection. Other tubers, if they have broken surfaces or 
wounds and lie in contact with affected ones, will also be 
infected. The rotten roots are therefore often found in 




Fig. 126. — Sweet potato soft rot. Original. 



groups through the pile. This rot is sometimes found in 
the field, but is not usually destructive until after digging. 
Normally it cannot enter a sound potato; a wound must 
furnish it a passageway. Therefore all wounded roots 
should be laid aside for immediate consumption, and only 
sound roots put in storage. 



VEGETABLE AND FIELD CROPS 291 

The following directions for storing are given by a person 
of extensive successful experience. Divide the cellar into 
slatted stalls 6 feet wide, 3 to 4 feet deep, with a foot 
between stalls. If the stalls are one above another, 
leave 6-inch spaces between them. In a large cellar 20 
or 30 by 50 or 75 feet, leave a 3 or 4 foot hall and 
build bins on each side. Take the sweet potatoes directly 
from the field to the cellar and put in bins 3 or 4 feet deep. 
If the ground is wet, sun for a time, so that the dirfc will fall 
from the potatoes. Whenever the thermometer registers 
40° F. above zero, especially at night, keep all ventilators 
wide open ; but should it rise above 65 ° F. outside, close all- 
ventilators tight, for hot air in the cellar will condense mois- 
ture or cause potatoes to become moist " sweat." Keep the 
inside temperature between 45 ° F. and 60 ° F. Never allow 
any part of this cellar to stand open when the air outside 
is 15° F. warmer than inside. Potatoes carefully sorted, 
then stored in well-constructed houses in the above manner, 
will not* rot. 

It is well to destroy all infective material, rotten roots, 
etc., in or near the storage place, and if the house is once 
infected, to spray its walls and floors thoroughly with a good 
disinfectant, such as Bordeaux mixture or formalin. 

Black rot (Sphceronema fimbriatum (E11.& Halst.) Sacc). 
— This is among the most destructive of all sweet potato 
decays, causing much loss in storage as well as in the field. 
Infected potatoes are bitter and worthless. Black rot has 
been reported from Indiana, New Jersey, Ohio, Tennessee, 
North Carolina, Maryland, and Alabama. 

The rot may be known by its dark brown to black, irregular 
patches upon the potato surface. These begin as points and 



292 



DISEASES OF ECONOMIC PLANTS 



gradually extend in all directions, involving the whole 
root. Older spots, 2-5 cm. across, often break or crack 
irregularly near the center. This 
decay differs from the soft rot in 
that the spots are dry and hard 
and that it is present upon the 
roots before digging. With the 
hand lens very small, hairlike, 
black structures, 1 mm. high, are 
seen studding the centers of the 
diseased areas. These are the 
beaks of the pycnidia of the causal 
fungus. 

Upon young sprouts before they 
are set out the disease causes black, 
dead patches, especially at the base 
of the shoot or even upon the young 
leaves. The wood of the stem may 
be browned. Such sprouts if set 
result in enfeebled plants with dis- 
eased roots. 

The fungus throws myriads of 
spores into the soil. This disease 
thus falls under the general class 
of soil diseases. 

In addition to the suggestions 
given on page 63, especial precau- 
tion should be exercised to avoid 
sets already affected. Badly af- 
fected shoots are easy of recognition, but the closest 
scrutiny is needed to cull out those only slightly affected. 




Fig. 127. — Black rot of sweet 
potato. Original. 



VEGETABLE AND FIELD CROPS 



293 



Above all, infected seed beds should 
be avoided, and no infected potatoes 
should be used for growing sets. 
Crop rotation should be practiced, 
and every precaution taken to get the 
plants well established in the field. A 
strong, well-started plant will often 
resist the disease where a weak plant 
would succumb. Waite 1 says : " The 
best remedy is to use slip seed. It is 
advisable to grow the crop of vine 
cuttings on new land which is not in- 
fected or on land which has never 
grown sweet potatoes, thus making 
an absolutely clean start even though 
the vine cuttings are taken from an 
infected crop." 

Soil rot (Acrocystis Batatce (Ell. & 
Halst.). — The loss from this rot is 
sometimes almost total, and since this 
is a soil disease, the raising of the crop 
is prohibited for several years. 

The roots are attacked when quite 
small, sometimes ]over the whole sur- 
face. The part infected ceases to 
grow, while adjoining parts enlarge. 
This results in a condition such as 
that shown in Fig. 128. The smallest 
rootlets are the points of attack, thence 
the disease proceeds to the potato and 
causes the surface spots pictured. 

1 Waite, M. B., Encyc. of Agr., II, 622. 



,# 



:'•''. 



tore 



Is 



& 



M_> 



Fig. 128. — Soil rot of 
sweet potato. After 
Halsted. 



294 DISEASES OF ECONOMIC PLANTS 

The chief loss is in the cessation of growth resulting 
from the disease. In badly infected fields no potatoes 
of marketable size mature, and the crop is not worth 
harvesting. 

Long rotation to avoid placing sweet potatoes upon 
infected soil is advised. 

Halsted 1 shows that soil rot, even upon land badly in- 
fected with the fungus, can be controlled by sulphur and 
kainit ; 400 pounds of each applied to the soil when the new 
roots are to form gave the best results. Treated plats 
gave 60 bushels of clean potatoes as contrasted with 5 
bushels for the untreated plat. 

Wilt, stem rot, nectriose (Nectria Impomcece Halst.). — 
In this disease, reported from New Jersey, California, 
North Carolina, Ohio, and Illinois, the stem dies near the 
surface of the ground, and the decay extends into the pota- 
toes and vines. The whole vine dies unless supported by 
roots at some other place. Following the death of the 
original stem, the portion of the root still alive throws out 
a fresh growth of short stems and leaves near the center of 
the hill. Such efforts at recovery are valueless. 

Rotation is necessary. 

Dry rot (Phoma Batatce (Ell. & Halst.). — In dry rot, 
the affected part, often the upper end of the potato, 
becomes dry, much wrinkled, and covered with numerous 
pycnidia, the flesh within changing to an almost powdery 
condition. From an economic point of view the rot is 
unimportant; still, affected potatoes should be destroyed. 

Dry rot, lasiodiplodiose (Lasiodiplodia tubericola Ell. & 
Ev.). — The potatoes show dark, shriveled patches with 

1 Halsted, B. D., N.J. Agr. Exp. Sta. Rpt. 1898, 350. 



VEGETABLE AND FIELD CROPS 295 

scattered pycnidia. 1 The tissue within is spongy, moist, 
and from olive-gray to green in color. In the United 
States the disease was first noted in Louisiana on po- 
tatoes received from Java. It has also been noted in 
Florida. 

Scurf (Monilochcetes infuscans Ell. & Halst.). — A brown 
or rusty coat often forms over the whole potato. It 
causes no decay, but does result in shrinking, loss of 
volume, and unsightliness, which may reduce the money 
value of the crop a half dollar per barrel. The same affec- 
tion occurs upon the roots from which the potatoes arise, 
but seems to do little or no damage there. 

Blue mold, penicilliose (Penicillium sp.). — The diseased 
parts are of almost chalky color and consistency, dry and 
inoffensive. Until the root is cut this rot may escape 
observation. It may be first seen as a slight depression 
in the roots at the base of a fine fiber. These depressions 
enlarge and deepen and may involve the whole potato. 
In sections of these spots the diseased portion is found to 
have a dark border which upon exposure to the air 
rapidly changes to a dark olive color. 

Leaf spot, leaf blight, phyllostictose (Phyllosticta bata- 
ticola Ell. & Mart.). — Spots of dead tissue from 1-10 mm. 
in diameter are frequent upon the leaf. They are some- 
what angular, very definitely bordered, and bear numer- 
ous pycnidia, visible to the naked eye. In many instances 
these spots become so numerous as to cause the whole leaf 
to yellow and fall and thus seriously interfere with starch 
production, and lessen the crop. 

Spraying with Bordeaux mixture would probably stop 

1 Clendenin, Ida, Bot. Gaz. 21, 92, February, 1896. 



296 DISEASES OF ECONOMIC PLANTS 

the disease, but the outlay might not be warranted except 
in special instances. 

White rust (Albugo ipomcece-pandurance (Schwein.) 
Swingle) . — White, glistening sori, 1 mm. or so in diameter, 
appear upon the undersides of the leaves, and upon 
the stems. These rupture and set loose a mass of powdery, 
snow-white spores. The tissue surrounding the sorus is 
pale, or yellow, as seen from the opposite side of the leaf. 
The tissue surrounding old sori dies, and brown patches 
result. 

No large injury usually comes from the disease. 

TOBACCO 

Root rot (Thielavia basicola (B. & Br.) Zopf.). — Known 
in Europe since 1897, thielaviose was first reported in 
the United States in 1904, as occurring upon tobacco, 
though it has probably been long prevalent in tobacco 
sections. It has been noted upon other hosts; namely, 
violets in Connecticut, Maryland, and District of Columbia ; 
ginseng in Ohio and New York; also upon begonia, catalpa, 
and clover. Upon tobacco it is now known in Ohio, Con- 
necticut, Kentucky, and North Carolina, and its territory is 
increasing yearly. 

Thielaviose in the seed bed often causes the entire crop 
of seedlings to be discarded, delaying planting or compelling 
a change of crop. In the field the loss sometimes amounts 
to 25 per cent. 

The disease is recognized by the black decay upon the 
roots, sometimes a cracking and deformation on the stem 
just above the roots, and the failure of the plant to develop 
normally. 



VEGETABLE AND FIELD CROPS 



297 



Damping off may occur upon seed beds. The plants are 
attacked when very young, and death may result before 




Fig. 129. — Tobacco roots showing effect of thielaviose. After Gilbert. 



they attain a height of more than 5-10 mm. In other cases 
of milder attack the roots alone are invaded and the plants 



298 DISEASES OF ECONOMIC PLANTS 

stunted. The tips of the rootlets are brown or black, and 
the entire root system is involved later. The decayed 
roots become so brittle that they are severed and remain 
in the ground when the plant is pulled. Numerous 
lateral rootlets are put out to replace these lost, but these 
also succumb sooner or later. The leaves of diseased seed- 
lings on rich soil are usually abnormally dark green. They 
may, however, in poor soil be of a sickly yellow color. 

In the field the diseased seedlings may remain for weeks 
without growth; some yellowing, wilting, and dying. 
Some in light soil may survive and yield a fair, but late, 
crop; in heavy soil few survive to be of value. When 
large roots are attacked, the effect is generally limited to 
the outer surface, where a brownish, scurvy appearance is 
produced. 

Sick plants in healthy soil or healthy plants set in sick 
soil result in diseased crops, and the development of the 
disease when the causal fungus is present is favored by 
alkaline fertilizers. 1 

To avoid loss from this disease only uninfected plants 
should be used; to procure these an uninfected seed bed 
must be secured and maintained. 

An infected seed bed can be rendered safe by disinfec- 
tion by the means suggested under soil disinfection, select- 
ing the method best applicable to the conditions. Surface 
firing is the method most widely used in connection with 
the tobacco crop. Formalin has also proved successful 
in many instances. 

The following measures conduce to reduction though 

1 Gilbert, W. W., U.S. Dept. Agr. Bur. Plant Indus. Bui. 158, 
1909. 



300 DISEASES OF ECONOMIC PLANTS 

not to complete eradication of the disease : The use of 
light rather than heavy soils for the seed bed; avoidance 
of excess of water or fertilizer ; the use of a new bed each 
year ; avoidance of too heavy seeding. 

Infested fields should be given a rotation to relieve them 
of tobacco temporarily. 

Granville wilt, bacillose (Bacillus solanacearum E. F. 
Smith 1 ). — This wilt was first noted in print in 1903, 2 
and it was first attributed to bacteria in September of the 
same year. 3 It was known to tobacco growers in Granville 
County, N.C., at least as early as 1881. It takes possession 
of the soil, prohibiting successful tobacco culture in succeed- 
ing years, and in sections where tobacco is the chief, possibly 
the only, profitable money crop the advent of this disease 
has caused great depreciation in farm values. 

The wilt is now known in North Carolina, Florida, 
Georgia, possibly Connecticut, and what appears to be 
the same disease has been described in Cuba, Porto Rico, 
France, and Japan. 

The first indication of the disease is given through the 
leaves, which droop, becoming soft and flabby as though 
suffering from want of water. This is not accompanied by 
change in color ; the leaves remaining green for some time 
after the wilt appears. A typical case is shown in Fig. 131. 
Frequently the leaves on one side of the plant succumb 
earlier than those on the other side, and even a single leaf 
may show one-sided infection. The wilted leaves dry up, 

1 Smith, E. F., U.S. Dept. Agr. Bur. Plant Indus. Bui. 141, part II, 
1908. 

2 Stevens, F. L., N.C. Agr. Exp. Sta. Press Bui. ll, August, 1903. 

3 Stevens, F. L., and Sackett, W. G., N.C. Agr. Exp. Sta. Bui. 188, 1903. 



VEGETABLE AND FIELD CROPS 



301 



and eventually leaves and stalk die, though the stalk re- 
mains standing with its dead leaves still clinging to it. 




Fig. 131. — Tobacco plant in early stage of the Granville wilt. Original. 

At the stage of earliest wilting a section across the stem 
shows a yellowish discoloration of the woody portion. In 



302 



DISEASES OF ECONOMIC PLANTS 



more advanced stages, or in sections taken lower on the 
stem, the wood is found to be penetrated longitudinally by 
black streaks which are so abundant in stages immediately 

preceding death 
that the whole or 
nearly all of the 
wood seems to be 
so affected. Simi- 
lar streaks pene- 
trate the pith only 
in extreme cases. 
The blackening 
often progresses 
from the wood out- 
ward through the 
bark, producing 
shrunken, black- 
ened patches on 
the surface of the 
stem. 

In more ad- 
vanced stages, 
when all the leaves 
are wilting, the 
wood and bark at 
the base of the 
plant are blackened almost throughout, and the pith is 
decayed, leaving the stem hollow or filled with a soft, 
rotten residue. The bark, near the level of the ground, 
turns black, and becomes dry and hard. The pith and 
wood in the upper portions of the plant usually dry up, 




Fig. 132. 



•Tobacco plant in late stages of the Gran- 
ville wilt. Original. 



VEGETABLE AND FIELD CROPS 303 

resulting in collapse in irregular longitudinal folds. If a 
badly diseased plant is cut off near the ground, a dirty 
yellowish viscous exudate issues from the cut wood. 

The root is the seat of the original infection, and any 
plant which shows symptoms in its foliage possesses roots 
already in pronounced stage of decay. In early stages one 
root or more may be diseased ; in later stages all succumb; 
in the more advanced stages of root disease the bark is 
black, soft, and dry, a spongy mass of fiber left by the decay 
of the more watery parts. In the worst cases even this 
spongy covering may drop off, leaving the wood of the root 
bare. 

In the root as in the stem the disease manifests itself first 
as longitudinal streaks of black in the woody cylinder close 
to the bark. 

No corrective for a field once infected is known. After 
infection the only recourse would be to resistant varieties, 
if such were known, or to long rotation, and this is unsatis- 
factory and palliative only. 

The means by which this disease spreads from field to 
field, and methods to prevent such spreading, are suffi- 
ciently discussed under soil diseases. 

Cercpsporose (Cercospora Nicotiance Ell. & Ev.). — 
This disease, most abundant upon the lower leaves, is 
well illustrated in the accompanying figure. It appears 
as brown, circular spots from the size of a pinhead to 
a centimeter or more in diameter, thickly scattered over 
the leaves. Older spots bear white centers bordered by a 
darker raised line, and the centers often fall away, leav- 
ing irregular holes. The whole leaf yellows and ripens 
prematurely. 



304 DISEASES OF ECONOMIC PLANTS 

The disease was first 
described by Sturgis 1 
from specimens sent from 
South Carolina. It was 
then very destructive, 
practically ruining the 
crop. A damage of $1000 
to one crop alone was 
noted. It has since con- 
tinued as a troublesome 
pest. 

The use of Bordeaux 
early in the season is per- 
missible and advanta- 
geous. 

White speck (Macro- 
sporium tabacinum Ell. & 
Ev.). — White speck con- 
sists of small, circular 
spots, rusty red or brown 
at first, but later with 
blanched centers, upon 
which the scattered hy- 
phse grow. 

Brown spot (Macro- 
sporium longipes Ell. & 
Ev.). — This spot differs 
from the above in its rusty 

Fig. 133. — Tobacco leaf showing leaf spot . . . . 

(cercosporose). After Conn. Exp. Sta. brOWn Color and in having 

1 Sturgis, W. C, Conn. State Agr. Exp. Sta. Rpt. 20, p. 273, 1896. 




VEGETABLE AND FIELD CROPS 305 

concentric markings. It is known to planters as the brown 
spot. 

Bed rot, rhizoctoniose (Rhizoctonia sp.). — Damping off 
and rot of seedlings while in the seed bed occur in this 
disease. The causal fungus may often be seen as spots 
of web-like white mold upon the ground around the affected 
plants. The general characters and prophylaxis are dis- 
cussed under damping off and rhizoctoniose. Seed beds 
known to be diseased should be avoided unless disinfected 
before use. 

ft Stem rot (Botrytis longibrachiata Oud.). — In this curing- 
house disease pure white, velvet-like patches of mold appear 
upon the stem, spread rapidly to the veins, and cause leaf 
decay, especially in the regions of the ribs and veins and 
other parts that dry but slowly. 

The causal fungus matures its spores in great quan- 
tity upon the refuse stalks and stems, and thus persists 
from year to year. 

To prevent the disease all refuse should be gathered and 
burned as soon as the crop is cured, and the floor and barn 
disinfected with Bordeaux mixture or bluestone. 

Drop, damp off, sclerotiniose {Sclerotinia sp.). — Damp- 
ing off due to sclerotinia is reported by Clinton 1 as a 
common trouble in seed beds. The injury to the plant 
is similar to that of the usual damping off, p. 60, while 
the fungus presents the characters described under lettuce 
sclerotiniose. Young plants are killed; older plants may 
survive, and if set in the field, develop poorly. 

Poleburn, pole rot. — Poleburn is a curing-house disease 
occurring on hung tobacco. In warm, damp weather the 

1 Clinton, G. P., Conn. State Agr. Exp. Sta. Rpt. 1896, p. 326. 
x 



306 DISEASES OF ECONOMIC PLANTS 

chief symptom consists in small blackened areas upon the 
leaf, limited at first to the regions near the vines. These 
spots may enlarge within two days to cover whole leaves, 
and the contents of the entire barn may become worthless, 
the leaf having become so wet and soft as to readily fall 
apart. 

The disease is known in Connecticut, Virginia, Kentucky, 
etc. In some sections it occurs yearly in more or less de- 
structive form. Its cause is not certainly known; indeed 
there may be several separate organisms, each capable of 
inducing the rot. 

The trouble can be largely controlled by proper regula- 
tion of the moisture and temperature conditions, i.e., by 
building such barns that the air of outdoors, when too 
damp, can be kept out, and yet with proper provision for 
ventilation to carry Off the moisture from the drying tobacco. 

Mosaic, calico, frenching. — The tobacco mosaic is very 
widely distributed and destructive. Depreciation of 
$50,000 in quality was attributed to it in Ohio in 1905. 
It causes a mottled appearance of the leaves due to va- 
riation in texture and greenness; parts of the leaf show- 
ing full green and normal thickness, other spots pale or 
yellowish green, and thin. Accompanying these signs are 
distortions due to unequal growth, wrinkled or curled 
leaves, and leaves of one-sided growth. Slightly affected 
leaves are depreciated in value; badly diseased leaves are 
worthless. 

This disease is not perfectly understood, but it seems to 
be communicable from plant to plant by first touching a 
diseased plant and later touching a healthy one. Thus 
the disease is spread largely by topping. It is known also 



VEGETABLE AND FIELD CROPS 307 

to be transmitted by means of soil that has grown a sick 
crop. Fertilizers which cause rapid growth favor the dis- 
ease. 

The seed bed should be either new or well disinfected, and 
it is advisable to destroy diseased seedlings in the bed if any 
appear. Young plants should not be forced with strong 
nitrogenous fertilizers and should be transplanted with 
great care to avoid injuring them. It is well to top, worm, 
and sucker the healthy and sick plants separately, on dif- 
ferent days, with disinfection of the hands before passing 
from the diseased to the healthy plants. 

Orobanche. — This is a true flowering plant, which draws 
its nourishment from the roots of the tobacco plant to 
which it is attached. The orobanche occurs in small 
clusters, its stalks are from 1-4 dm. tall, arid entirely de- 
void of green color. 

They should be pulled and burned before they produce 
seed. 

TOMATO 

Wilt, blight, bacillose (Bacillus solanacearum E. F. Smith). 
— This disease of the tomato is widespread, especially in 
the South, and prohibits the raising of tomatoes upon many 
thousands of acres of land. It occurs especially in the 
states south of Maryland, and has also been noted in New 
Jersey, Delaware, Ohio, and Colorado. 

In this disease the leaves wilt, either singly or through- 
out the entire plant at once; growth stops and the plant 
dies. The stem is at first dirty green, then brown, then 
black. It soon shrivels, and the veins become brown and 
show as narrow black lines, or in section as black dots. 



308 



DISEASES OF ECONOMIC PLANTS 



The wilting of the foliage and the blackening of the bun- 
dles are distinctively characteristic. 1 

A soil bearing diseased plants one season is subject to 
the malady in succeeding years and must be abandoned 
for tomato culture. The disease is spread from plant to 
plant largely by the potato bug (Colorado beetle) and other 




Fig. 134. — Tomato field showing effect of wilt (bacillose). Original. 



insects. For this reason all leaf-infecting insects should be 
given special attention. Otherwise this disease in symp- 
toms, cause, dissemination, and treatment is similar to the 
usual soil diseases. 

Wilt, fusariose (Fusarium sp.). — A form of fusariose has 
been described in California by Smith 2 as follows: It 
occurs not infrequently as the cause of losses up to 100 

1 Smith, E. F., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 12, De- 
cember 19, 1896. 

2 Smith, R. E., Cal. Agr. Exp. Sta. Bui. 175, January, 1906. 



VEGETABLE AND FIELD CROPS 309 

per cent of plants between half-grown and maturity. In 
1905 the disease was probably more general than ever 
before, completely ruining many fields in southern Califor- 
nia. The plants usually reach considerable size, blos- 
som, and set fruit before showing the disease, which first 
appears in the field on -single plants, which are generally 
sickly looking, and of unhealthy color, followed by 
symptoms of wilt. The leaves do not blacken or sud- 
denly die, but the whole plant gradually sickens, loses 
color, wilts, and finally collapses upon the ground. The 
disease comes on gradually in the field, affecting plants 
here and there in a very scattering manner. In the worst 
cases they all die before the summer is over, sometimes 
quite suddenly at the last ; again, the field goes through in 
a spotted condition, with plants missing more or less ex- 
tensively. If a badly affected or dead plant be pulled up, 
the roots are found to be decayed or destroyed. When first 
affected, this is not the case ; if a plant is pulled up as soon 
as it begins to show wilting and fading, the roots look 
healthy and sound. But if such plants be carefully dug, 
to avoid breaking off the smaller roots, it will be seen that 
many of the larger laterals are decayed at the ends and are 
in bad condition. The disease consists of a dry rot of the 
roots, commencing at the ends and working upward. 

The first symptom is a pale yellowish color of the 
lower leaves, which soon dry from the tip toward the 
base without spotting. The veins and woody portion of 
the stem, if examined in cross section, are darkened, espe- 
cially upon the side bearing the diseased leaf. The disease 
progresses from the old leaves to the youngest, resulting 
eventually in the death of the plant. 



310 



DISEASES OF ECONOMIC PLANTS 



As to means of dissemination and control, what is said 

under soil diseases will apply. 

Leaf mold (Cladosporium fulvum Cke.). — Under glass 

in the North and occa- 
sionally in the open, 
especially in the South, 
this disease is destruc- 
tive. It occurs as 
rusty or cinnamon- 
brown blotches on the 
lower side of the leaf, 
which turns yellow 
above, then brown or 
black, curls, and dies. 
The loss of food sup- 
ply consumed by the 
parasite together with 
the loss through de- 
struction of the leaf 
green injures the yield 
seriously. 

Indoors, ventilation 
is the best remedy, 
coupled with clean cul- 
ture to avoid carrying 
the pest over to an- 
other year. On fields 

Bordeaux mixture would doubtless serve well. 

The causal fungus of this disease was first described in 

1883 by Cooke from specimens collected in North Carolina. 
Leaf spot (Septoria Lycopersici Speg.). — A very com- 




Fig. 135. 



-Tomato leaf showing spots (sep- 
toriose). Original. 



VEGETABLE AND FIELD CROPS 311 

mon leaf spot has almost precisely the general appear- 
ance illustrated in Fig. 135, except that small pycnidia 
occupy the spots. 

The disease attacks the older leaves first and works 
toward the top of the plant, often causing the loss of so 
many leaves as to give the plant the appearance of blight, 
and resulting in complete ruin of the crop. The presence 
of the leaf spot distinguishes this from any of the blights. 
Spraying with Bordeaux mixture is effective against this 
disease though valueless against the various wilts. 

Cylindrosporiose (Cylindrosporium sp.). — This disease 
in general appearance, damage, and treatment resembles 
septoriose. See above. 

Downy mildew, blight (Phytophthora infestans (Mont.) 
DeBy.). — Arising from the same cause as the dreaded po- 
tato blight, of which host the tomato is close kin, is the 
very injurious tomato blight, causing complete devastation 
of the crop in some sections, and resulting in a loss of many 
thousands of dollars. It has been reported in Massachu- 
setts, Colorado, and is serious in California. 

As is the case with the potato, the amount of damage 
is closely dependent upon suitable weather conditions, the 
disease being greatly favored by a warm, humid atmos- 
phere. It appears suddenly as dark, discolored spots on 
the fruit and other green parts. On the fruit the spot, 
usually upon the upper side, is watery and large. Many 
tomatoes, apparently healthy when picked, rot in shipment, 
the rot being accompanied, under humid conditions, by 
a fine, white surface mold. Dark spots upon stems and 
branches soon extend throughout the whole plant, giving 
it the appearance of one stricken by frost. 



312 DISEASES OF ECONOMIC PLANTS 

Protective spraying with 5-5-50 Bordeaux mixture, as 
recommended for the potato, will probably serve in case of 
this disease. In regions of infrequent rainfall it is neces- 
sary to spray only after each rain. 

Blossom-end rot, point rot. — Readily recognized from its 
name, this very troublesome disease is essentially a dry, 
black rot appearing on the blossom end and injurious 
chiefly to early tomatoes. It is especially harmful, owing 
to the high value of the early fruit that it destroys. 
Various fungi and bacteria have been named as the cause, 
and it cannot yet be said with certainty which is the 
guilty one. Perhaps it is one, perhaps several. In any 
event it seems to be an infective disease that is probably 
carried by insects. 

The trouble is more serious upon droughty soils and can 
be to some extent controlled by irrigation or moisture 
conservation, i.e., increasing the water-holding power of 
the soils by the addition of organic matter and surface 
tillage. 

Black spot, rust (Macrosporium Solani Ell. & Mart.). — 
Ruin is brought to the crop in many seasons, particularly 
in the southernmost states, by black spot, which is possibly 
identical with the potato early blight. The leaves bear 
numerous small, usually angular spots, often concentrically 
marked, which appear first as minute brown specks, later 
showing a pale center with a darker border. In badly 
affected leaves the tips dry and curl up. Petioles and 
stems are also attacked. 

Thorough spraying with the usual Bordeaux mixture 
should be begun at the first indication of the disease and 
continued weekly, or semi-weekly if growth is rapid and 



VEGETABLE AND FIELD CROPS 



313 



weather damp. Often it is still better to begin spraying 
in the seed bed. 

Southern blight (Sclerotium Rolfsii Sacc. in litt.). — 
This is the same disease discussed under pepper. Upon 
the tomato it is often completely destructive in the south- 
ernmost states. 

The first sign is wilting of the terminal portion of the 
plant, distinguishing this 
trouble from the fungous 
wilt, which commences 
with the lower leaves. 

For discussion and 
treatment see pepper. 

Anthracnose (Colletotri- 
chum phomoides (Sacc.) 
Chest.). — This is chiefly 
a disease of the ripe fruit, 
either upon the vines or 
after harvest. It appears 

as sunken, discolored spots with wrinkled surfaces and black 
specks, the acervuli. The disease does much damage to 
fruit before it is picked, and also injures the keeping quality. 

Fumagose (Fumago vagans Pers.). — Dense, olive-black 
growths of mold form upon the leaves, but little or no 
harm is done. 

Damping off. — Tomatoes in the seed bed are subject to 
damping off. 

(Edema. — This is a condition of overgrowth of certain 
cells of the plant, causing swelling of veins and leaf tissues, 
and curling of the leaves in irregular growth. Usually 
confined to the greenhouse, it is caused by excess of water, 






Fig. 136. 



Tomato anthracnose. 
Heald. 



After 



314 DISEASES OF ECONOMIC PLANTS 

lack of light, improper temperature, and especially by too 
warm soil, and is readily controlled by careful management. 

Mosaic. — Upon the tomato appears a disease very 
similar to the mosaic of tobacco. Aside from this ap- 
parent kinship little is known about it. 

Rosette (Rhizoctonia sp.). — This rosette is possibly 
identical with the potato rosette, 1 showing similar lesions 
upon the root and stem near the ground. The tops have 
long internodes and dwarfed leaves which are somewhat 
curled. For further discussion see potato. 

Upon the ripe fruits, especially those touching the ground, 
this disease occurs as a brown rot upon a slightly wrinkled 
epidermis. 

TURNIP 

Black rot (Pseudomonas campestris (Pamm.) E. F. Smith). 
— It was upon this crop in 1892 that the disease, now 
known in so destructive a form upon the cabbage and 
other cruciferous crops, was first noted by Pammel. 2 It 
then caused 10 per cent loss ; the next year 50 per cent, 
and it has since been known to cause total ruin in many 
instances. 

The rot is recognized by the blackened veins in the 
crown, root, leaf stems, and leaves. The softer tissue 
near such veins is abnormally watery, and the interior of 
the root undergoes dry decay with a characteristic strong 
odor. The cavities thus made are of peculiar radiate 
form, with black or brown walls. Diseased plants may 
live for considerable time with apparently healthy leaves, 

1 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 145, November, 1903. 

2 Pammel, L. H., la. Agr. Exp. Sta. Bui. 27, 1895. 



VEGETABLE AND FIELD CROPS 315 

but the roots grow very slowly and assume an abnormal, 
narrow shape. The badly rotted hollow root may show 
no external signs of the disease. 

The character, dissemination, and control of this disease 
are discussed under cabbage. 

Club root. See cabbage. 

Powdery mildew (Erysiphe polygoni DC). — This pow- 
dery mildew is often a serious pest in England, but seems 
to be much less injurious in America, though it has fre- 
quently been seen in this country, forming conspicuous 
white patches upon the surface of the leaves. 

Macrosporiose (Macrosporium herculeum Ell. & Mart.). — 
Numerous small, white spots occur upon the leaves, each 
spot later with a slight, black, moldy growth in the center. 

Treatment is not warranted. 

Scab. See potato. 

White rust. See cabbage. 

Downy mildew. See cabbage. 

The two last-mentioned diseases often occur together 
and in such form as to cause considerable loss. If plants 
are badly affected, it is well to collect and burn all diseased 
refuse and to rotate crops. 

WATERMELON 

Wilt, fusariose (Fusarium vasinfectwn Atk. var. niveum 
Sm.). — The melon wilt not only destroys the growing crop, 
but prevents the successful culture of melons upon the field 
in question in succeeding years. The disease has spread 
rapidly during the past decade and is now known in most 
of the southeastern United States ; also in Iowa, Oklahoma, 
California, Oregon, Indiana, Kentucky, and Arizona. 



316 DISEASES OF ECONOMIC PLANTS 

The wilt is readily recognized from the fact that the 
leaves first droop, as though they were suffering from want 
of moisture, rapidly wilt, and soon die, the runner dying 
with the leaves. Soon the whole plant is dead. Upon 
cutting the main tap root across near the surface of the 
ground, such plants are found to present a yellow color 
in the wood, making a distinct contrast with the white 
color of the healthy plants. This one character, taken 
together with the wilted appearance of the vine, enables 
recognition of the true watermelon wilt. The further 
fact that a field once infected shows the same disease in 
succeeding years in the same or in extended areas is an 
additional recognition mark. 

Its spread may occur in the ways mentioned under soil 
diseases and in particular through the use of infected 
manure. 

To restrict it to its present confines crop rotation should 
be practiced and infected soil should not be replanted to 
watermelons until the wilt fungus is largely diminished in 
quantity. This will probably take more than four years, 
possibly eight or ten years, and even at the end of that time 
it is best to try a few hills before planting the whole field 
to melons. Cattle should not be allowed to pasture upon 
diseased vines and thus spread the wilt through the manure. 

The practice of raising cowpeas after watermelons leads 
to the presence of some watermelon vines in the cowpea 
hay, and this likewise leads to the presence of the causal 
fungus in the compost heap. Manure so exposed to infec- 
tion should never be placed on land which is still free from 
the germ, or which is to be used to raise watermelons, 
since this is a sure way of spreading the wilt. 



VEGETABLE AND FIELD CROPS 



317 



There is no objection to the use of stable manure which 
does not contain the fungus, but experience has shown 
that when the wilt 
once gains entrance 
to the compost 
heap or barnyard, 
it remains there for 
years, and all of 
the manure taken 
out of such a yard 
is likely to spread 
the disease. Hence 
it is exceedingly 
dangerous in re- 
gions where the 
wilt prevails to use 
any stable manure 
on the field where 
melons are to be 
planted. 

Varieties resist- 
ant to this disease 
have been devel- 
oped by the United 
States Department 
of Agriculture by 
crossing the citron, 
which possesses high resistance, with the watermelon, and 
then by selection attaining the desired edibility. 

Wilt, bacillose. See cantaloupe. 

Wilt, micosphaerellose. See cantaloupe. 




Fig. 137. 



— Portion of watermelon showing effect of 
anthracnose. After Sheldon. 



318 DISEASES OF ECONOMIC PLANTS 

Anthracnose (Colletotrichwn lagenarium (Pass.) Ell. & 
Halst.). — This disease attacks all parts of the vine, 
sometimes causing complete failure of the crop. Its most 
conspicuous form is upon the fruit at any age, especially at 
maturity. Here very characteristic sunken spots with pink 
centers, much like the bean-pod spot, are produced. Upon 
old melons they do but slight injury, but to young fruit 
the attack is often fatal. A bitter taste is often imparted 
to the sick fruit. 

Upon the stems while yet green the spots are irregular, 
elongated, light brown. Tendrils, buds, and petioles turn 
black and die. The leaves instead of yellowing, as with 
downy mildew, are covered with dark blotches of dead 
tissue which becomes brittle and often tears out. 

Spraying as for the downy mildew is effective. It is 
also well to destroy infective refuse and to practice rotation. 

Downy mildew. See cucumber. 

C.ercosporose. See cantaloupe. 

Alternariose. See cantaloupe. 



CEREALS 

Cereal Smuts in General 

These diseases show themselves to the farmer as dark 
to black, dusty or hard, masses occupying the places where 
the grain should be or involving also the near-by flower 
parts, glumes (chaff), etc., and in some cases the leaves 
and stem as well. The smut mass consists almost wholly 
of the spores of the causal fungus. This fungus gains 
entrance to the plants when they are in a susceptible con- 
dition of development, the time varying with different 
kinds of plants, and grows within the plant as an active 
parasite, drawing its nourishment from its involuntary host. 
When the host plant has attained the proper age, and 
correspondingly, too, the fungus has reached its proper 
stage of maturity, the disease becomes apparent to the 
eye as the only too familiar smut. 

Smut spores under suitable conditions of moisture, food, 
and heat sprout, and produce smaller spores, sporidia, 
which, if they fall upon the proper host plant in the proper 
period of its development, penetrate into it and grow. 
The host plant may or may not outgrow its enemy. In 
any event, its presence is not apparent to the naked eye 
until the period of maturity arrives again, and another 
crop of dark-colored spores is produced. 

Kinds of smut. — In all* there are many kinds of smuts. 
Something more than 600 species are now recorded. Over 

319 



320 DISEASES OF ECONOMIC PLANTS 

205 of these are found in the United States, growing upon 
some 442 different kinds of plants. 1 

Most smuts are upon unimportant, uncultivated plants. 
Some of them, such as the corn smut, onion smut, and the 
smuts of wheat, oats, rye, barley attack plants of high eco- 
nomic value and cause great damage. The common corn 
smut develops upon almost any part of the corn plant, 
but is usually most conspicuous upon the ear and tassel. 
Onion smut grows upon the leaves, often in the bulb; rye 
smut in the stem; that of oats, wheat, and barley in the 
ovary, the grain. Another smut of corn growing upon 
the tassel is less widely known. 

It is evident that to know precisely at what parts and 
at what periods the various crop plants are open to infec- 
tion is of utmost importance in looking to the prevention 
of the smuts. It was early proved that oats are suscep- 
tible to infection only in the very young periods of their 
development. Kuehn and Wolff held opposing views as 
to whether it is the young stem or the first leaf sheath that 
is susceptible. The very exact work of Brefeld settled 
this point beyond all controversy. He also proved that 
corn is susceptible to infection on all young, tender, growing 
parts, and recently Macldox, Brefeld, and others have 
shown that in the case of the loose smut of wheat and the 
barley smut infection occurs while the plant is in bloom, 
this infection affecting the seeds and resulting in smutted 
plants in the crop raised from such infected seeds. 

It is upon these facts that our present modes of preven- 
tion are based. The treatment for oat smut is such as to 
kill the spores adhering to the grain and thus prevent in- 

1 Clinton, G. P., Proc. Boston Soc. Nat. Hist. 31, 334, 1904. 



CEREALS 



321 



fection during the period of susceptibility, i.e., the very- 
young seedling condition. The same treatment is effec- 




Fig. 138. — Oat plants, smutted and healthy ; note difference in height. 
Original. 

tive for the stinking smut of wheat. The loose smut of 
wheat gaining entrance to the plant before the grain 



322 DISEASES OF ECONOMIC PLANTS 

is harvested cannot be prevented by such means with- 
out danger to the seed, but can be prevented by the 
use of clean, uninfected seed. Corn, being susceptible 
at all ages of its growth, cannot be protected by seed 
treatment. 

Owing to their great damage and conspicuousness, smuts 
have attracted attention from very early times, and many 
references to them are found in ancient writings. Prob- 
ably not until 1791, however, was their true nature as 
vegetable parasites recognized. Many were the means 
that were suggested for the prevention of these pests: 
placing laurel branches in the field, change of seed, avoid- 
ance of manures, thorough screening, soaking in brine, etc. 

Preventive treatments. — The only one of the early 
treatments that has proved its value and remained in 
common use is that of soaking the seed in copper sulphate 
(bluest one), first tried by Tessierin 1789, after he, in 1786, 
and Young, in 1787, had tested numerous chemicals. His 
test was without results, since during that season neither 
treated nor untreated wheat was smutted. Prevost of 
France in 1807 was the first to publish an account of the 
successful use of bluestone for wheat smut. He recom- 
mended a solution of about 6 per cent strength, and the 
remedy was, and is still, widely used. Solutions varying in 
strength have been employed, one half per cent being most 
highly recommended. In 1873 Dreisch improved the blue- 
stone treatment by using limewater to follow the blue- 
stone; thus, to a large extent, diminishing the amount of 
seed killed by the treatment. 

Jensen, a Dane, in 1887 and 1888 reported excellent 
results with oat, barley, and wheat smuts from dipping 



CEREALS 323 

the seed in hot water. Untreated seed gave 36 per cent of 
smut. One fourth per cent of bluestone gave one half per 
cent smut. Warm water, 133° F. for five minutes, gave no 
smut. Kellerman and Swingle soon afterward introduced 
this last treatment into this country. 

In 1888 the germicidal action of formalin was discovered 
and this substance was used as a preventive for oat smut by 
Bolley of North Dakota during the three years preceding 
1897. 

The Sar treatment was first announced by Swingle in 
1898. 1 

The use of the various smut remedies is usually attended 
by an increase in vigor of the plants, and by an increase 
in yield in excess of that due simply to the elimination 
of the smutted grains. The reason for this has not been 
fully explained, but it may be due to elimination of the 
fungus from plants which otherwise would have to resist 
it throughout a portion of their growth period in order to 
overcome it and to eventually bear grains. An excellent 
account of the early history of smuts in general may be 
found in the Report of the Kansas Agricultural Experi- 
ment Station for 1889, and a comprehensive article upon 
corn smut in the Twelfth Report of the Indiana Agricul- 
tural Experiment Station. 

Cereal Rusts in General 

The rusts constitute a complex, intricate, difficult, but 
interesting group of diseases. It is said that the " average 
annual loss from rust throughout the United States far 

1 Swingle, W. T., U.S. Dept. Agr. Farmers' Bui. 75, p. 15. 



324 DISEASES OF ECONOMIC PLANTS 

exceeds that due to any other enemy, insect or fungous, 
and often equals those from all others combined." x 

The rust of wheat alone is estimated by Bolley to cause 
an average loss in the United States of $20,000,000, while 
Galloway placed the loss in 1891 at $67,000,000. 

The rusts in their most complete form exhibit three dis- 
tinct stages (cf. asparagus) : the spring stage, or cluster 
cup, consists of a group or cluster of very minute, cup- 
like, spore-bearing regions, sori. These cups are sunken 
in the tissue of the host, often with their rims only pro- 
truding. The second stage, summer stage, also called 
the uredo stage, is of entirely different appearance, con- 
sisting usually of elongated sori, bearing a mass of 
spores the color of iron rust or verging towards orange or 
yellow. These spore masses are at first covered by the 
epidermis of the host, but this covering eventually rup- 
tures, disclosing the usually dusty or pulverulent mass of 
spores, surrounded by a fringe of the remaining epidermis. 
The third stage, winter stage, or teleutospore, consists of 
sori almost exactly like those of the uredo stage except 
that the spores within are usually darker in color and in 
a compact, cushion-like mass, therefore lending to the 
sorus a considerable alteration in aspect. The sorus is 
often identical in the two latter stages, a uredosorus grad- 
ually changing as the season advances into a teleutosorus. 

These three stages have in general three separate func- 
tions. The function of the teleutospores is to live over 
winter or over the long resting period of the fungus. They 
are essentially long-lived and hardy. The cluster-cup 

1 Carleton, M. A., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 16, 

p. 19, September 27, 1899. 



CEREALS 325 

spores are to multiply and spread infection, especially in 
the earliest part of the season. The uredospores are to 
continue the multiplication and infection throughout the 
growing season of the host. The last two forms of spores 
are in general comparatively short-lived. If the host plant 
remains alive over winter, as is the case with winter wheat, 
the fungus, south of the fortieth parallel, may continue 
to grow and produce summer spores all winter, and the need 
of the other two forms is lessened. Even in colder climates 
the uredospores of some rusts live over winter and start in- 
fection in the spring. 

In the case of some rusts these three forms are all present 
and are known to man. In the case of other rusts one 
stage or even two stages may be either unknown or may 
not exist at all. When all three stages do exist, the spring 
stage is often upon some host other than that bearing the 
uredo and teleuto stages. Thus the spring stage of the 
wheat rust is upon the barberry; of corn upon oxalis; 
of oats upon buckthorn. 

That some intimate relation existed between the bar- 
berry bush and the wheat rust was believed very early 
in the eighteenth century, and in 1760 Massachusetts 
passed a law placing a ban upon the barberry. In 1818 
Schroeter, a Danish school-teacher, published many obser- 
vations concerning the relation of the cluster cup upon the 
barberry and the rust of grains. This relation was finally 
definitely proved by DeBary in 1864, who, by sowing the 
teleutospores from the wheat upon the barberry, produced 
the cluster cups. 

All cereal rusts multiply much more rapidly in damp 
than in dry weather, and the most destructive rusts are 



326 DISEASES OF ECONOMIC PLANTS 

worse upon late crops. There is no evidence that these 
maladies can be carried by seed from rusted plants, though 
such seeds should not be used for seed purposes, since they 
do not have stored nourishment sufficient to give the 
seedling a vigorous start. 

Great difference in rust resistance has been shown; thus 
one variety was so badly affected as to yield only 2f 
bushels per acre, while a resistant variety under the same 
conditions gave 38} bushels. 1 

The greatest hope lies in the use of varieties which can 
resist the disease. A number of varieties of the different 
kinds of grain are now known which possess sufficient 
resistance to give good yields even when the rust is in its 
worst epidemic form. Since serious epidemics of rust 
must be looked forward to with certainty, the item of rust 
resistance must have due weight in the selection of the 
variety to be grown. 

Several varieties of oats, among them Texas and Georgia 
Rust Proof, are known to possess valuable, though not 
complete, resistance to the oat rust when grown in the 
Southern States, though the same resistance is not main- 
tained under the different climatic influences of the North. 

Early maturity in oats is of especial value in that it 
enables the plant to evade the heaviest part of the rust 
attack. Good drainage conduces to plants of more resist- 
ance to rust, as does also good preparation of the seed bed 
and extermination of weeds. Drilled wheat is better 
lighted and better ventilated and resists rust better than 
wheat that is broadcast. 

Wild grasses that harbor rusts identical with the rusts 

1 Carleton, M. A., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 16. 



CEREALS 327 

of crop plants, such as wild meadow oat grass, orchard 
grass, wild wheat grasses, quack grass, wild rye grasses, 
etc., may propagate the fungus and increase infection. If 
such grasses are rusted, they should be burned, plowed 
under, or avoided in the location of the grain fields. 

While sprays of various kinds may be effective in checking 
the spread of rusts, the use of such means of prevention is 
impracticable, owing to the nature of growth of the crop, 
and the difficulty and expense of the application. Moreover 
the question of use of such treatment is complicated by the 
different kinds of rusts to be met and by their different 
behavior in different seasons. 

Anthracnose of Cereals 

Anthracnose (Colletotrichum cereale Manns 1 ). — Upon 
many cereals and forage crops, as rye, wheat, oats, orchard 
grass, timothy, red top, and blue grass, occurs a blight, 
resulting in shriveling- of the grain and spotting of the 
leaves and stalks. The fungus is marked by small, black 
acervuli, located upon the spikes, stems, and sheaths, and 
the chief attack is made as the plants approach maturity. 

For more complete discussion, see rye. 

Special Diseases of Cereals 
BARLEY 

Loose smut (Ustilago nuda (Jens.) Kell. & Sw.). — 
This disease, previously thought insignificant, seems to 
be increasing in importance. It now often causes losses in 
Wisconsin and Minnesota of from 5 to 10 per cent of the crop, 

1 Sci. n. s. 29, 915, June 4, 1909. 



328 



DISEASES OF ECONOMIC PLANTS 



and is present to some extent in most fields of this country, 
though often unnoticed on account of the early season of 




Fig. 139. — Loose smut of barley in various stages of development. After Johnson. 



its development, and its absence at harvest time. Every 
spikelet of the smutted head is usually affected and entirely 



CEREALS 329 

changed into smut, the central stalk of the head alone 
escaping. Adjacent leaves are also occasionally smutted. 

The smut masses, when they first appear, are covered by a 
white or gray membrane which soon ruptures, loosing the 
powdery olive-brown mass of spores, which soon blow 
away. This character enables one to distinguish this with 
ease from the covered smut. Smutted plants head early, 
the smut reaching its maximum at flowering time, though 
scattered heads of smut may appear at other dates. The 
smutted heads stand high on especially tall stalks, which 
affords excellent wind distribution of the spores to the 
surrounding blossoms. The fungus reaching the blossoms 
gains such foothold upon the developing grain that its use 
as seed, without treatment, insures a smutted seedling as 
offspring. In the plant developing from such an infected 
seedling the disease does not show externally until the 
ripening of the smut at the next blossoming season. 

The life history of this smut is thus similar to that of 
wheat loose smut, and the same treatment, i.e., rouging, 
combined with a modified Jensen hot-water treatment, 
is effective, preventing all the smut. See p. 372. 

Covered smut ( Ustilago Hordei (Pers.) Kell. & Sw.). 
— In the covered smut, the smut masses occupying the 
place of the grains and glumes are at first covered by a 
membrane composed of the outer surface of the glumes 
of the spikelet. This membrane retains the spores for 
some time after harvest. The spores, as seen en masse, 
after the rupture of this cover are very dark to purplish 
black, with no tint of olive. 

The treatment given for oat smut applies here. 

Ergot. See rye. 



330 DISEASES OF ECONOMIC PLANTS 

Black stem rust (Puccinia graminis Pers.). — Identical 
with that on wheat, this rust can be readily transferred 
from either host to the Other. See wheat. 

Scab (Gibberella) . See wheat. 

Yellow leaf disease (HelminthosporiumgramineumTlhh.). 
— This leaf blight was discovered in America by Pammel 
in 1890. It is characterized by longitudinal, yellowish 
green spots in parallel rows upon the leaves. The plants 
die prematurely, and the yield is thus reduced. 

Helminthosporiose (Helminthosporium sativum Pamm., 
King, & Bakke). — First known in 1907, this disease has 
been observed in Iowa, South Dakota, Minnesota, and 
Saskatchewan. 1 

It occurs as brownish, circular or somewhat elongated, 
dark spots which soon cause the leaves to turn brown. It 
also occurs upon sheaths, glumes, spikelets, and grain. 
The straw at harvest is dull brown and lacks strength. 

Powdery mildew. See wheat. 

BROOM CORN 

Kernel smut (Sphacelotheca Sorghi (Link) Clinton). — 
This fungous disease of broom corn and sorghum is indi- 
cated by the presence of irregular elongated branches of 
very inferior value. The branches are further damaged by 
the blackening occasioned by the loose spores. The seeds 
are, of course, destroyed. Of the fields examined by Clinton 
in Illinois 2 few showed over 1 per cent of the stalks in- 
fected, though sometimes parts of a field bore as high as 20 

1 Pammel, King, and Bakke, Am. Phytopath. Soc, 1st Ann. Meet- 
ing, December 31, 1909. 

2 Clinton, G. P., 111. Agr. Exp. Sta. Bui. 47, March, 1897. 



CEREALS 331 

per cent of infected stalks. Infection can occur only upon 
very young plants. Between the times of infection and 
the appearance of the smut masses in the panicle no signs 
of the disease are seen without the aid of the microscope. 

The smut can be prevented by the use of clean seed, 
obtained either from clean fields or by disinfecting the 
seed by the hot water (135° F. for 10 to 15 minutes) or 
formalin methods, as given for oats. 

Head smut. See sorghum. 

CORN 

Smut (Ustilago Zeos (Beckm.) Ung.). — Corn smut is 
well known to every farmer, occurring everywhere the 
corn plant is grown, as black, pulverulent masses most 
conspicuous upon the ear and tassel. The damage done 
by it is estimated at 1 per cent of the ears. To this should 
be added perhaps 1 per cent more to cover the loss in vigor 
that is sustained by the plant. Under exceptional con- 
ditions the damage may exceed these figures. Thus in 
Iowa a loss of two thirds of the crop was at one time re- 
ported. 

Corn smut is first mentioned in literature in 1754, and 
the first American record is that of its collection in North 
Carolina in 1822. Experiments looking to its prevention 
were made as early as 1760. The disease may attack any 
part of the plant at any age, — leaves, stalks, aerial roots, 
ears, tassels, — provided only that they be still in tender 
growing condition, not mature and hard. 

The first symptom is a pale, glistening, swollen area 
covered with a white membrane, which soon appears black 
owing to the maturation of the spores within. The mem- 



332 



DISEASES OF ECONOMIC PLANTS 



brane eventually bursts, loosening a powdery, dry, black 
mass of spores through which fibrous veins of the corn 

plant still pene- 
trate. It has been 
conclusively dem- 
onstrated that the 
causal fungus is not 
conveyed to the 
new crop in the 
seed, as is the case 
with so many other 
smuts, and that 
therefore no form of 
seed treatment is of 
value for its pre- 
vention. The sow- 
ing of seed covered 
with smut spores 
does not result in 
any more smut than 
does the use of un- 
infected seed. 

It has been clearly 
shown that infec- 
tion is produced by 
the spores which, 
under suitable con- 
ditions of moisture, 
fall upon any tender 
part of the corn plant. The silks furnish the requisite 
conditions, and it is through them that ear infection occurs. 




Fig. 140. — Corn smut upon the ear. Original. 



CEREALS 



333 



The sheaths of the leaves hold water, and inclosing as they 
do the tender growing portion of the stem, are admirably 




Fig. 141. — Smut upon sweet corn tassels. After Jackson. 



suited to infection. Other portions of the plant are less 
suited to the requirements of the fungus and are not so 



334 DISEASES OF ECONOMIC PLANTS 

often attacked. Since infection cannot occur without mois- 
ture, weather conditions are of predominating influence. 

The longer the crop grows, the longer the period of sus- 
ceptibility is maintained. Thus a late-planted crop in 
Indiana showed half as much infection as a crop which 
was planted earlier, chiefly because it was exposed to con- 
tagion only about half as long. Moisture and richness 
of soil predispose to disease by increasing growth and giv- 
ing a greater number of susceptible points of attack. Corn 
thickly planted is more liable to infection because venti- 
lation is restricted, and thus a more humid atmosphere is 
created around the plants. 

It has been shown that corn smut can be reduced some 
16 to 72 per cent by spraying with Bordeaux mixture, but 
the saving does not warrant the expense. The only practical 
method is to go through the field several times during the 
season and cut out and burn all the developing smut masses 
that can be seen, to thus destroy the spores and prevent 
the continued spread of the disease. Professor Bessey says : 
" The cost per annum of gathering and burning the smutted 
ears ought not to exceed ten or fifteen cents per acre. A 
smart boy carrying a bag slung over his shoulder ought 
to be able to earn good wages in smutting corn at ten cents 
per acre." This practice continued yearly would result 
in continued diminution of smut. Whether it will be profit- 
able or not depends upon the amount of smut usually found 
in any given community. The use of the silo in which the 
smut spores are destroyed tends to lessen the amount of 
smut. The smut fungus can live and even increase in 
manure. Therefore live smut spores may infect the ma- 
nure pile and thereby increase the disease in fields to which 



CEREALS 335 

such manure is applied. The smut itself, contrary to 
popular belief, is poisonous only under very rare and ex- 
ceptional conditions, so rare as to be practically negligible. 
Head smut (Sphacelotheca Reiliana (Kuehn) Clinton). — 
This smut, identical with that of sorghum, occasionally 
occurs upon corn and is somewhat more injurious than the 
usual corn smut. 

Corn Ear Rots 

Four types of ear rot due to four distinct diseases 
are described below. In the aggregate the loss from 
these is enormous, constituting as it does 10 per cent 
or more of a crop worth annually more than $125,000,000. 
The infection resulting in this loss comes from definite 
species of fungi, and is not comparable to ordinary molding 
of dead organic matter by fungi of varying kind. These 
corn ear rots are true definite diseases. Ninety per cent 
of these rots is caused by one species of fungus alone, 
and its vulnerable points of attack are known. 

Dry rot (Diplodia Zece (Schw.) Lev.) and (Diplodia 
macrospora Earle) . — This is one of the very widespread 
dry ear rots of corn variously known to growers as mold, 
mildew, rot, dry rot, etc. Suspicion has been recently cast 
upon it as the cause of pellagra. 1 

Though the disease is really present soon after silking, 
and even much earlier from root infection, it is not usually 
recognized until husking, when a whitish covering of the 
kernels within the husk is noted. This white mycelium 
also forms dense masses between the individual grains, 
among the husks, and over the cob. The grains on the 

1 Smith, E. F., and Hedges, Florence, Sci. n. s. 30, 60, July 9, 1909. 



336 



DISEASES OF ECONOMIC PLANTS 



t , 



Fig. 142. — Young ear of 
corn inoculated in the 
silk with diplodia. 
After Burrill & Barrett. 



affected ear are shrunken, loosely at- 
tached, light in weight, and darker in 
color and more brittle than those of a 
healthy ear. Upon breaking open an 
ear, very small black pycnidia may be 
seen embedded in the white masses of 
mycelium, especially at the bases of 
the kernels. Diseased ears left in the 
field may develop these pycnidia in 
such abundance as to make the grains 
black. 

Much of the food value of the corn 
is lost, owing to the consumption of 
starch within the grain, as well as to 
the prevention of starch storage. The 
germinating power of the grain is also 
lost. 

Upon the stalks the fungus first 
appears as very small dark specks 
under the rind, near the nodes, and 
at broken places, usually in over- 
wintered stalks. Stalks nearly three 
years old have been found bearing 
pycnidia. Although the green stalks 
are not naturally susceptible, the shanks 
are particularly so. 

The causal fungus gains entrance 
to the ears from infected stalks which 
bear them, and these are infected from 
the soil through the roots. Ears are 
also infected through the silks by wind- 



CEREALS 



337 



borne spores, which come, in part, from diseased ears, but 
more largely from diseased stalks left in the field. 



bS ™" " J*N> 




■;..-. 




*&.. i 


* " ' '44| 


«i , 




1 




H '-" ; jfl 


P: ■ 




?v 


1 1 


<* 



Fig. 143. — Diplodia on old shanks. After Burrill & Barrett. 



Any method of reducing the amount of infective trash, 
particularly old stalks near or in the fields, aids in control 



338 



DISEASES OF ECONOMIC PLANTS 




Fig. 144. — Corn mold caused by 
Fusarium. After Burrill & Barrett. 



of this pest. Practically, this 
means to take out of the field 
and destroy all rot-infected 
ears and to cut infected stalks 
low and haul them away or 
burn them. It is still better 
to practice such rotation that 
corn will not follow corn 
within two years. Badly in- 
fected fields or spots in fields 
should never be planted to 
corn without rotation. 

Dry rot, fusariose (Fusa- 
rium). — Upon the ears this 
disease appears as a dense, 
felted, white mycelium, ex- 
tending between the kernels 
to the cob. The kernels are 
killed and their starch partly 
consumed. 

A second fusarium disease 
is characterized by a deep 
pink to red color noted on the 
ear when the husks are re- 
moved. The kernels are brit- 
tle and the starchy portion 
powdery. 

A third fusarium disease 
causes less complete destruc- 
tion of the ear than the pre- 
ceding; often only a few 



CEBEALS 339 

scattered kernels are affected. The mycelium is white and 
sparse. 

Blight {Bacterium sp.). — This disease was under the 
observation of Professor Burrill of Illinois for some time 
prior to 1889 and was described by him in that year. 

It shows chiefly as a dwarfed condition which may occur 
upon plants scattered throughout the field or more often 
upon plants in certain spots in the field, such sick spots 
varying in size from a few rods to an acre or more. The 
affected plants appear abnormally slender, finally cease 
growing, turn yellow, and most of them die. In rare 
instances they may recover. 

The lowest roots of diseased plants, in some cases com- 
prising half of the root system, are dead or dying. The 
stalk near the base, when split lengthwise, shows a uni- 
form dark color which also appears in the upper nodes 
in lesser degree. The internodes show no disease symp- 
toms. Upon the surface of the stem base are brownish, 
corroded spots, diffuse or definitely bordered, and ac- 
companied frequently by masses of rather firm semi- 
transparent jelly. 

The leaf sheaths show watery brown or red specks or 
larger irregular patches. Upon the insides of the sheaths 
these spots are more conspicuous and larger, and are coated 
with a gelatinous substance. 

The ears are sometimes affected in plants which are 
taken with the disease so late as to allow ears to form. All 
parts of the ear appear wilted and gelatinous coated, and 
the silk rotten, though not ill scented. 

Wilt, pseudomonose (Pseudomonas Stewarti E. F. 
Smith). — This corn wilt was first described by F. C. Stew- 



340 DISEASES OF ECONOMIC PLANTS 

art 1 as prevalent in nearly all parts of Long Island upon 
many different varieties of sweet corn. In some cases the 
entire crop was ruined, and 20 to 40 per cent of loss was 
frequent, though in the majority of cases the loss was so 
slight as to pass without notice. 

The diseased plants wilt and dry up much as though for 
want of water, yet in soil that is amply water supplied. 
While the wilting is most liable to occur at flowering time, 
it may appear at any stage of growth when the plants are 
25 cm. or more in height. In mild cases the lower leaves 
wilt first, while in severe cases all wilt at one time. The 
death of the plant may come in four days after the first 
signs of disease show, or may be delayed a month, possibly 
with recovery and relapse intervening. 

The roots remain normal, but the veins in the stems 
appear as yellow streaks, in older cases black, instead of 
their normal color. Such stems, if cut crosswise, shortly 
exude a yellow, viscid drop at the ends of the veins. This 
is the most distinctive character, and infallibly indicates 
the presence of the wilt. Death is caused by the plugging 
of the water passages with this viscid substance, which con- 
sists mainly of bacteria. 

In the fields the diseased plants are scattered unevenly, 
young and old stages and healthy plants together, health 
and disease even in the same hill ; yet there appears to be no 
direct plant-to-plant infection, nor any of that centrifugal 
spreading from a diseased center that is so noticeable in 
most wilt or soil diseases. 

The causal organism is found in the seed from affected 

1 Stewart, F. C, N.Y. (Geneva) Agr. Exp. Sta. Bui. 130, December, 
1897. 



CEREALS 



341 



plants, and it has been proved experimentally that such 
seed carries the disease 
to the offspring. 1 

As a preventive meas- 
ure resistant varieties 
should be selected for 
planting, and all seed 
from plants which are 
at all diseased should be 
avoided. The disease 
may be carried from one 
locality to another by 
any of the means sug- 
gested under soil dis- 
eases, and especially by 
manure infected with 
stalks of diseased plants. 

Rust (Puccinia Sorghi 
Schw.). — Corn rust 
seems to have taken its 
place in literature in 
1815. It is of compara- 
tively slight harm, since 
it does not usually 
develop early in the 
season, though in ex- 
ceptionally favorable 
climatic conditions it 
may develop early upon 
young plants. Its injury is then greater. The loss is en- 

1 Smith, E. F., Sci. n. s. 30, 223. 




Fig. 145. 



Portion of corn leaf showing sori of 
rust. Original. 



342 DISEASES OF ECONOMIC PLANTS 

tirely in destruction of green tissues and impairment of 
starch-making power. 

The sori, confined almost entirely to the leaves, are those 
characteristic of the rusts, the brown summer spores appear- 
ing first in linear sori, and the black winter spores coming 
later in the season. The cluster-cup stage is found upon 
the wood sorrel (Oxalis). 

Yellow leaf disease, helminthosporiose (Helminihosporium 
inconspicuum C. & Ell.). — This blight gives a somewhat 
frost-bitten appearance to the plants, producing also a thin 
olive-green mold upon the lower sides of the leaves. Some- 
times only the tips of the leaves are affected, but usually 
whole leaves die. 

The disease produces elongated yellowish spots limited 
by the veins. The spots are sometimes covered with dark- 
colored spores. The disease is confined almost entirely 
to late-planted corn, and is prevalent during its early 
growth, though it has never been reported upon seedlings. 

It is known to cause much loss in Delaware, New York, 1 
and Connecticut, 2 and is of widespread occurrence in the 
United States. 

Sclerospofose (Sclerospora macrospora Sacc). — This 
causes considerable injury to corn in Italy. It has been 
collected in the United States, but has not been serious. 
The tassel is chiefly affected. 

MILLET 

Piriculariose (Piricularia grisea (Cke.) Sacc). — Upon 
the lower leaves the disease occurs as a spot which is 

1 Stewart, F. C, N.Y. (Geneva) Agr. Exp. Sta. Rpt. 15, 452. 

2 Conn. State Agr. Exp. Sta. Rpt. 13, 171, 1889. 



CEREALS 



343 



at first dark purple or reddish and 
elongated, parallel with the length of 
the leaf. Later the center turns black 
and finally straw-colored, bordered by 
a black ring which merges into red- 
dish purple at its outer edge. 1 Badly 
diseased leaves turn yellow and dry 
and shrivel from the tip toward the 
base, lessening the fodder value and 
seed yield of the plant. 

Smut (Ustilago Crameri Koern.). — 
This smut infects the individual flow- 
ers, destroying the lower parts of the. 
glumes. It has been noted in Ohio, 
Minnesota, Connecticut, Illinois, Indi- 
ana, Iowa, Maine, Michigan, North 
Dakota, and South Dakota. 

The formalin treatment as recom- 
mended for oat smut is applicable. 

OAT 

Loose smut (Ustilago Avence (Pers.) 
Jens.). — Under the name "smut," 
"blackheads," etc., this disease is 
known wherever oats are grown. Grain 
and more or less of the chaff are re- 
placed by a powdery black mass, which 
shatters out as it ripens, leaving later 
only the naked branches of the panicle. 

1 Jackson, Del. Agr. Exp. Sta. Bui. 83, Decem- 
ber, 1908. 



Fig. 146. — Leaf spot of 
millet due to piricula- 
riose. After Jackson. 



344 



DISEASES OF ECONOMIC PLANTS 




Usually all the spike- 
lets of a head and all 
the heads of the 
affected plant are 
smutted. There is 
considerable difference 
in the resistance of- 
fered by different va- 
rieties, but in view of 
the perfect protection 
afforded by proper 
treatment this is of 
little significance. 

The damage caused 
by smut is usually 
underrated. In 1884 
Arthur 1 in New York 
by actual count found 
the oat smut to con- 
stitute 'from 8.5 to 10 
per cent of the ordi- 
nary crop. By actual 
count of nearly 11,000 
heads Plumb 2 in 1886 
determined the amount 
of smut to be 8.4 per 
cent ; in some fields he found as high as 20, 28, and even 30 
per cent. Kellerman and Swingle, 3 counting smutted heads 

i Arthur, J. C, N.Y. (Geneva). Agr. Exp. Sta. Rpt. 3, p. 382, 1884. 

2 Plumb, C. S., N.Y. (Geneva) Agr. Exp. Sta. Rpt. 5. 

3 Kellerman, W. A., and Swingle, W. T., Kans. Agr. Exp. Sta. Rpt., 
p. 213, 1889. 



Fig. 147. — Smut (Vstilago avenoe) on oats. 
After Jackson. 



CEREALS 345 

in Kansas, found different fields to have 8, 15.3, and 18.3 
per cent of smut, while single portions of a field showed as 
high as 39 per cent. The annual loss in this country is 
somewhere between $10,000,000 and $20,000,000. 

The reasons for underestimation of oat smut are the 
dwarfing of many of the affected plants: which thus re- 
main unnoticed by a casual glance over the field, and the 
fact that many smutted panicles remain invisible unless 
unrolled from their enveloping leaves. 

It was proved as early as 1858 that infection can occur 
only upon the very young oat plant: that older plants 
are immune. It was later determined by Brefeld that 
the plants are immune after the leaves have protruded 
1 cm. beyond the leaf sheath. From this it follows that 
the chief (and as other experiments have demonstrated 
practically the only) infection comes from smut spores 
which are upon the seeds when they are planted. These 
sprout, producing sporidia which infect the young plant. 
The fungus develops in these plants throughout the 
season without conspicuous effect until, at blossoming 
time, the fungus seeks the ovaries and the glumes and ap- 
pears again as the familiar black spore masses. 

Any treatment which kills the spores upon the seed with- 
out materially injuring the seed itself results in a clean crop. 

The bluestone treatment so widely used to prevent wheat 
smut, however, is not advisable for oats, since its use is at- 
tended with too much danger to the germinating power of 
the oat seed. The hot-water treatment as applied to wheat 
for loose smut, using a temperature of 132°-133° F. for 
ten minutes, 130° F. for fifteen minutes, or 145° F. for not 
more than five minutes, may be employed with perfect 



346 DISEASES OF ECONOMIC PLANTS 

efficiency ; but since the formalin or Sar treatments are 
thoroughly satisfactory and much easier of application, 
the latter are preferable. The formalin treatment may be 
made as follows : — 

Formalin can be purchased from a druggist at a cost of 
from seventy-five to ninety cents per pound, much cheaper 
if purchased in quantity. One pound is sufficient to treat 
forty-five to fifty bushels of grain. It should be used at 
the rate of one ounce to three gallons of water, and in gen- 
eral, one gallon of mixture suffices to treat one bushel of 
grain. 

Spread the grain in a thin layer on a smooth barn floor, 
canvas, or upon hard ground, and sprinkle with the diluted 
formalin, using either a spraying machine or a watering 
pot. Sprinkle so as to thoroughly and evenly wet the grain 
with the mixture. Then shovel the grain over thoroughly 
a few times to insure even distribution of the solution and 
thorough wetting of all the seeds, and cover the pile with 
canvas, carpets, blankets, or bagging, to keep the fumes of 
the formalin within. The pile should stand from six to 
twelve hours in this way. The seed may then be readily 
dried by mixing with air-slaked lime, and the lime may be 
removed by the fanning mill, or the lime may be omitted 
and the grain dried by spreading it out in layers about 
5 cm. thick and stirring it frequently. The seed is then 
ready to sow. It may be stored, but in so doing it is 
liable to renewed smut infection, unless all bags, bins, etc., 
with which it comes in contact are also disinfected with a 
thorough application of the formalin solution. The drill 
that is used should also be disinfected either with formalin 
or by a thorough dusting with dry lime. 



CEREALS 347 

On a large scale oats have been treated by the formalin 
method at the rate of 500 bushels an hour, by throwing the 
formalin solution, by means of a steam pump, against the 
grain as it fell through elevators arranged with deflectors so 
as to give proper mixing. 

The Sar (sulphur, alkali, resin) solution has the ad- 
vantage that the necessary ingredients can be procured at 




Fig. 148. — Outfit and mat for preparing Sar solution. After Swingle. 

places where it might be difficult to buy formalin ; other- 
wise formalin is preferable. 

To make the Sar treatment, take one half pound of or- 
dinary resin and powder it finely, then mix thoroughly with 
15 pounds of ordinary flowers of sulphur. When thor- 
oughly mixed add, little by little, about six quarts of water, 
stirring all the time. At first the mass crumbles when 
stirred, but when the right amount of water has been added, 
the sulphur and resin make a stiff paste, which does not 
crumble or flow. Too much water must not be added. 
This paste should be made in the bottom of a barrel or 



348 DISEASES OF ECONOMIC PLANTS 

large keg holding at least six times the bulk occupied by the 
paste, and preferably more. 

Now pour out ten pounds of granulated caustic soda 
(concentrated 98 per cent lye or caustic potash) and throw 
it on top of the sulphur-resin paste and stir rapidly and 
thoroughly with a flat paddle. In a few minutes the paste 
begins to turn a reddish brown and slowly liquefies and 
in a few seconds turns into a deep brown liquid and boils 
violently. It should be stirred all the time, and after a min- 
ute or so it will cease boiling. Hot water should then be 
added slowly with stirring until the solution is brought up 
to a six-gallon mark previously made on the inside of the 
barrel. 

This constitutes the stock Sar solution. It should be 
allowed to stand a few moments, until any dirt or uncom- 
bined sulphur has settled to the bottom, and then dipped 
off and stored in jugs, tightly corked. The mixture can be 
preserved for months without deterioration. Only a few 
ounces of the sulphur will remain in the barrel if the solu- 
tion has been properly prepared. 

One fourth of the above formula can be made in a candy 
pail as shown in Fig. 148. This gives H gallons of stock 
solution, or enough for 75 gallons of the solution ready for 
use, in which the grain is soaked for two hours. 

The oats or wheat should first be thrown into water, and 
any smut balls which float should be skimmed off, stirring 
the grain to be sure that all the smut balls come to the top. 
The water may then be drained off and the grain treated 
with well-shaken Sar solution, 1 quart to 50 gallons of water. 
This should be stirred well in a barrel, then poured over the 
grain until it is covered several inches deep, stirring so that 



CEREALS 



349 



all the kernels are wetted. The grain 
should be left from ten to fifteen hours in 
the solution and stirred several times dur- 
ing the treatment. It may then be spread 
and dried. 

For large amounts of seed it is better 
to use a much stronger solution and for 
a shorter time (1 gallon of stock solution 
to 50 gallons of water for two hours). 

Covered smut, ustilagose ( Ustilago levis 
(Kell. & Sw.) Magn.). — This differs from 
the loose smut in the less complete de- 
struction of the flowers and in its less 
dusty spore masses, which are also blacker 
than in the loose smut. The smut masses 
are usually limited to the parts within the 
flowering glume and the palet or to the 
bases of these. 

The treatment is that given for Ustilago 
Avence. 

Black stem rust (Puccinia graminis 
Pers.). — The black stem rust on oats 
shows but slight differences from the black 
stem rust of wheat, but that it is at least 
racially distinct is indicated by the fact 
that proof by inter-inoculation has not 
been adduced and that a field of one of 
these crops may be badly affected by its 
fungus, while adjacent fields of the other crop show no rust 
or indication of infection such as they might be supposed 
to do were the two rusts identical. 



Fig. 149. — Smut 
(Ustilago levis) 
on oats. After 
Jackson. 



350 DISEASES OF ECONOMIC PLANTS 

More common and more injurious than the black stem 
rust of wheat, it constitutes the destructive oat rust, totally 
destroying thousands of acres of oats almost yearly. As 
with the wheat black stem rust, its attacks are epidemic, 
fluctuating greatly in abundance and destructiveness from 
year to year. It is usually more common in the northern 
states than in the South. 

Crown rust (Puccinia rahmni (Pers.) Wett.). — This 
rust is found only upon the various species of oats, and 
in the teleutospore stage clearly differs, even to the naked 
eye, from the other oat rust mentioned above, though 
in the uredospore stage such separation is extremely 
difficult without microscopic examination. 

It occurs upon oats in practically all fields and is more 
common than its more destructive relative, the black stem 
rust. Like the wheat orange leaf rust the damage done is 
not serious, or very rarely so. 

The cluster-cup stage of this rust is known to grow upon 
the common buckthorn (Rhamnus cathartica) and the 
lance-leaved buckthorn (Rhamnus lanceolatus) . The stage 
most conspicuous is the uredo, which forms numerous 
orange sori upon the leaves. Later the black teleutosori 
appear under the epidermis as long streaks which, unlike 
most rusts, do not rupture the epidermis. 

Marked varietal resistance is shown. In California 
black oats are reputed to be less subject to rust than white 
oats. In the North, the White Russian is said to be resist- 
ant, while in the South,' the Texas Rust Proof resists attack. 

Scab. See wheat. 

Phyllostictose (Phyllostictasp.). — Browned or reddened 
leaves with the black pycnidia profuse upon the affected 



CEREALS 351 

surfaces, sometimes so abundant as to lend a blackish 
hue to the leaf, comprise the diagnostic symptoms of this 
malady. Eventually the leaves are killed. 

Pseudomonose (Pseudomonas Avence Manns). — A disease 
prevalent throughout the entire Eastern and Central 
States was attributed to bacteria by Galloway and South- 
worth in 1890. 1 It appeared when the plants were only 
about 10" cm. high, first causing the leaves to turn brown 
and die at the tips, then throughout their length. The 
affected plants revived, but were so reduced in vigor as to 
prevent effective stooling, and a loss of 35 to 75 per cent of 
the crop followed. 

The disease has recently been carefully investigated by 
Manns, 2 who claims that it is caused by the symbiotic 
action of two species of bacteria, a pseudomonas and a 
bacillus. 

Manns describes the disease as follows : — 

The preliminary effect is yellowing of the leaf, beginning 
either as small, round lesions on the blade, or as long, streak- 
like lesions extending throughout the blade and even the 
whole length of the culm and blades. Occasionally it begins 
at the tips and works back into the culm ; again the upper 
leaves often break down through a weakened condition of 
the plant from defoliation below. 

The ultimate symptoms, wherever the disease has made 
much progress, are partial or general collapse of the leaves, 
which take on a mottled to almost red color. 

It prevails from New England to Georgia, and from the 
Atlantic to Indiana and Illinois. The damage in Ohio has 

1 Galloway, B. T., and Southworth, E. A., Jour. Mycol. 6, 72. 

2 Manns, T. F., Ohio Agr. Exp. Sta. Bui. 210, October, 1909. 



352 DISEASES OF ECONOMIC PLANTS 

been estimated at from 14 to 37 per cent of the crop. 
Rain and moisture favor it. 

When very prevalent, the soil may become infected as 
in typical soil diseases. The only hope seems to rest in 
resistant strains. 

Anthracnose (Colletotrichum cereale Manns) . — The effect 
of this disease upon oats is similar to that described for rye. 

Yellow leaf disease (Helminthosporium inconspicuum 
C. & Ell. var. brittanicum Grove). — Oat leaves with this 
disease turn yellow and pale and develop dark brown 
spore-bearing spots. Little is known as to its severity or 
prevention. 

Powdery mildew. See wheat. 

RICE 

Blast, rotten neck (Piricularia Oryzce Cav.). — This is a 
world-wide rice disease which in Italy is controlled by the 
use of resistant varieties. It has probably been present 
for many years in American rice sections, but did not 
become of serious economic importance until about 1895. 
What seems to be the same disease occurs upon crab 
grass, and apparently infection may come from this host. 
It is reported from South Carolina and Louisiana, also 
from Texas, where it has been serious. The disease occurs 
upon upland as well as irrigated fields. 

The most characteristic symptom consists of lesions at 
the sheath nodes just over the joints of the stem, at the 
region where the stem comes to be the axis of the head 
(the " neck region ") and at the points where the blades of 
the leaves join their sheaths, 1 appearing first as very small, 

1 Fulton, H. R., La. Agr. Exp. Sta. Bui. 105, April, 1908. 






CEREALS 



353 



water-soaked sunken spots on the node 
of the sheath. Spots upon the neck are 
not water-soaked, and the skin does not 
rupture until the head breaks off. Later 
the spot becomes brownish or black, and 
similar discoloration runs upward and 
downward. The affected stem tissue 
gradually extends laterally, shrinks, and 
dies, cutting into or through the joint, 
which results in an open wound. The 
region above the wound becomes pale 
and dies. 

Upon young plants leaf spots occur, 
first brown with ashen center, later coa- 
lescing and taking the whole leaf. If 
the attack is early, the grain does not fill 
at all; if late, it may partially fill. The 
dead portion of the plant may bleach or 
darken according to subsequent sur- 
roundings, resulting in great variety of 
appearances in the later stages of the 
disease. In 70 per cent of the cases ex- 
amined by Met calf 1 the lowest joint of 
the rachis was affected, and in conse- 
quence the heads broke off at this place. 
This gives rise to the common name 
" rotton neck," but since the character 
is not universal, the name is not an appropriate one. 

The chief damage results from the failure of the grain to 
fill on the diseased stalks. An early attack may render a 

1 Metcalf, Haven, S.C. Agr. Exp. Sta. Bui. 121. May, 1906. 
2a 



Fig. 150. — Rice blast. 
After Fulton. 



354 



DISEASES OF ECONOMIC PLANTS 



crop unworthy of harvesting. Plants attacked later yield 
some grains which are of poor, light quality, easily broken 
or blown away, and consequently largely lost in milling and 
threshing. The variation in size of the grain also largely 
depreciates the quality. Many of the heads, especially 
the heavier ones, fall off, and some fields show at least one 

third of the crop thus left 
upon the ground. 

The Rice Committee of 
the Agricultural Society in 
South Carolina, March, 1904, 
estimated the loss, up to 
that time, to be very nearly 
$1,000,000. Depreciation in 
land values, necessitating 
abandonment of land, is a 
not insignificant item of 
charge against this disease. 

While the disease can be 
stopped by spraying with 
5-5-50 Bordeaux mixture, 
this course is not practicable 
with such a crop as rice. The chief hope lies in the use 
of resistant varieties. Withholding nitrogenous fertilizers 
and removal of infective trash by burning are good sani- 
tary measures. 

Green smut (Ustilaginoidea virens (Cke.) Tak.). — This 
grain disease, though partaking of the appearance of a 
true smut, is in reality more closely related to the ergot of 
rye. The grains, usually only a few in each head, become 
enlarged, spherical, 5 mm. or more thick, and coated 




Fig. 151. — Rice showing " green smut." 
After Fulton. 



CEREALS 



355 



with a dark green powder. Sometimes a yellow color pre- 
vails instead of the green. In section the interior is seen 
to be filled with a compact white mass, bordered by a brown- 
ish yellow zone, then by the 
green coating. Though the 
disease has been known in 
Louisiana for ten or more 
years, and is there present to 
some extent in most fields, it 
is not considered serious, since 
rarely more than 0.25 per cent 
of the heads, and only a few 
grains per head, are affected. 

Black smut (Tilletia horrida 
Tak.). — A smut upon rice 
received by Anderson 1 from 
Georgetown, S.C., in 1898, was 
reported as darkening flour 
made from rice from affected 
fields. Many heads bore as 
much as 25 per cent of smutted 
grains. In Louisiana it is also 
reported, but not usually in 
amounts to cause much loss. 

This smut was probably imported from Japan in infected 
seed, but due to the immediate action of Anderson and 
Walker the pest seems to have been completely stamped 
out in South Carolina within the first few years after its 
advent. No reports whatever of its presence there have 
been made since 1903. 




Fig. 152. — Rice showing black smut. 
After Fulton. 



i Anderson, A. P., S.C. Agr- Exp. Sta. Bui. 41, March, 1899. 



356 



DISEASES OF ECONOMIC PLANTS 



The smut closely resembles the stinking smut of wheat. 
The affected ovaries or grains are transformed into stum 
masses which remain within the glumes, and so resemble the 
normal grains as to often be mistaken for them. The fungous 
mycelium grows within the stem tissue of the diseased 
plant, and, as is the case with wheat bunt, infection prob- 
ably occurs in the seedling stage, and the fungus remains un- 





Fig. 153. — Three rice spikelets ; A, normal ; B, smutted ; 
C, glumes partly torn away exposing the spore mass. 
After Anderson. 



noticed until its presence is disclosed in the place of the 
grain, as a black spore mass. 

The disease can be controlled, should it again appear, by 
the methods which stamped it out in South Carolina ; that 
is, by floating out and removing the light and smutted seeds 
in cold water, then soaking the seed for twenty-four hours 
in liver of sulphur, 11 pounds in 25 gallons of water, or by 
employing a 2 per cent solution and soaking the seed only 
two hours. 

Damping off. — Two forms of damping off of seedlings 
are known : — 



CEREALS 357 

1. Rice, not covered, but simply flooded with water, fre- 
quently shows soft rot of the shoot in very young seedlings. 

2. Covered rice often shows damping-off spots just above 
the surface of the ground. 

The causes of these rots have not been fully studied, but 
they are probably due to fungi or bacteria or both. 

Spotted blight (Macrosporium sp.). — Small black spots 
of mold upon poorly filled grains sometimes occur, occasion- 
ally affecting field areas of considerable size. Though this 
disease has been reported from South Carolina, North 
Carolina, Georgia, Alabama, Louisiana, and Texas, it is 
not seriously destructive. 

Speck, pip (Saprophytic fungi and bacteria). — The grain 
in some instances bears one or more discolored, often sunken, 
circular areas, 1-3 mm. in diameter, bounded by dark mar- 
gins with the centers gray or pale buff in color, and often 
with a minute dark spot in the very center. In other cases 
the grain is shriveled and distorted without any definite 
spot. The interiors of the grains are chalky and brittle, 
and of such inferior quality as to be largely depreciated 
in value. Not infrequently 10 to 25 per cent of the 
grain is affected, and in some cases nearly 100 per cent. 
Their germinating power is much reduced. 

The disease is caused by the invasion of saprophytic fungi 
or bacteria into wounds caused by sucking bugs. Methods to 
control these insects have not been thoroughly worked out. 

Rust (Physiological). — The leaves die gradually, begin- 
ning with the tips of the lower ones. Red spots and 
streaks usually appear before the leaves lose their green 
color. The plants are dwarfed, the roots poorly developed, 
and the heads small and light. 



358 DISEASES OF ECONOMIC PLANTS 

RYE 

Ergot (Claviceps purpurea (Fr.) Tul.). — Ergot is widely 
known as a black or purplish body, several times larger 
than the seed of the affected plant, which displaces the 
ovary or grain. Ergot occurs commonly upon rye and 
wheat, and upon many other species of grass, as wheat 
grass, wild ryes, bluejoint, Kentucky blue grass, Canada 
blue grass, red top, timothy, and rye grass. Of the last 
named, one farmer reports 1000 tons of hay so badly 
affected as to be worthless. 

This disease is caused by the attack of a fungus upon the 
ovary while the plant is in bloom. The fungus invades 
and consumes the ovary and replaces it with the ergot, which 
consists of a dense mass of tangled, interwoven mycelium, 
a sclerotium. Ergots, when mature and under suitable 
conditions, germinate, sending forth several stalks each, 
with club-shaped, knobbed tops. From these the spores 
issue to infect susceptible plants then in blossom. For 
some days the fungus spreads from blossom to blossom by 
means of other spores, and each infected ovary results in 
another ergot. 

Loss to the grain and the damage to the plant are slight. 
Chief injury from ergot arises from its effect upon the cattle 
which eat ergotized grain or graze upon badly infected grass. 
The effects appear in the spring; animals become emaciated 
and rough haired as the result of continuous feeding of ergot 
through the winter. Continued symptoms of ergot poison- 
ing are tardy circulation in the extremities, gangrenous 
sores upon the teats or mouth, and sloughing off of parts 
of the tail, ears, or hoofs. Abortion may also follow as an 
additional effect. 



CEREALS 



359 



Fields should be examined for the presence 
of ergot. If large quantities be found, the 
grass should not be used for hay or pasture. 
Ergot can be lessened by cutting susceptible 
grasses about flowering time, thus checking 
the spread of the fungus. Badly infected hay 
lands should be burned over to destroy scle- 
rotia; roadside grasses should be cut often 
enough to prevent the formation of ergot, 
and seed should be examined to prevent the 
spread of ergot through this means. 

Black stem rust (Puccinia graminis Pers.). 
— This rust is perhaps identical with the black 
stem rust of wheat, and the description given 
in that connection applies here. 

Orange leaf rust (Puccinia rubego-vera 
(DC.).Wint.). — This rust bears a very close 
resemblance to the rust of similar name upon 
wheat, but in careful inoculation experiments 
it has been impossible to infect one of these 
hosts from the other. It is invariably present 
where rye is grown and is particularly abun- 
dant in the Southern States, though not- 
withstanding its universal presence it is not 
destructive. The uredo mycelium remains 
alive and continues to produce spores over 
winter in the leaf in the South, as it probably 
does in colder climates as well. It is possible 
that it is in this way carried from season to 
season by volunteer rye in the fields. The 
cluster-cup stage occurs upon a member of 



Fig. 154. — 
Leaf of rye 
showing or- 
ange leaf 
rust. Orig- 

[ inal. 



360 DISEASES OF ECONOMIC PLANTS 

the Borage family, but has 
never been found occurring 
naturally in America. 

Smut ( Urocystis occulta 
(Wallr.) Reb.). — Unlike 
most of the cereal smuts, 
this affects the stems and 
leaves, not the floral parts. 
It may be recognized by the 
usual dusty black spores, 
which occur especially at 
the joints. While this dis- 
ease does not (hrectly at- 
tack the grain, it does 
diminish the yield by weak- 
ening the plant. It has not 
as yet been seriously de- 
structive in this country. 

Anthracnose (Colleto- 
trichum cereale Manns). — 
A serious disease of cereals 
and other grasses, chiefly 
rye, wheat, oats, timothy, 
blue grass, red top, and or- 
chard grass, was discovered 
by Selby and Manns * in 
1908 and described in 1909. 

It seems to be a destruc- 
tive pest of very general dis- 

1 Selby, A. D., and Manns," T. 

Fig. 155. — Head of rye attacked by an- F v 0hio A S r - Ex P- Sta - Bul - 203 > 
thracnose. After Manns. April, 1909. 




CEREALS 



361 



tribution, being found in all the 
fields examined in Ohio. In one 
field it is estimated to have re- 
duced the yield from 75 bushels to 
25 bushels, and it is assigned as a 
prominent cause of shriveling, such 
as is often attributed to rust, as 
well as of whitening and blighting 
of plants preceding ripening. Upon 
the heads the disease resembles 
scab, with the exception that no 
rose-colored coating is present; 
instead black acervuli are found 
upon close examination. Parts of 
the head above the points of at- 
tack die. The portion of the head 

that is killed is a total loss, and the general decrease in 
vigor of the plant results in shriveled light grains. Upon 
stalks and leaf sheaths, beginning at the ground and extend- 
ing over several internodes, the acervuli may be so numer- 
ous as to cause blackening. 




Fig. 156. — Basal portion of 
rye plant showing anthrac- 
nose upon stem and leaf 
sheath. After Manns. 




Fig. 157. 



Normal rye kernels and shriveled ones due to anthracnose. 
After Manns. 



362 DISEASES OF ECONOMIC PLANTS 

Treatment is not yet known. 

Scab. See wheat. 

Powdery mildew. See wheat. 

SORGHUM 

Blight (Bacillus sorghi Burr) . — This blight was studied 
by Burrill in 1883 and described in 1887. It prevails upon 
sorghum, broom corn, Kaffir corn, and Milo maize, and 
has been noted in Illinois, Kentucky, Iowa, Louisiana, 
Ohio, Michigan, Nebraska, West Virginia, and District 
of Columbia, often in serious form. The chief character 
is irregular-shaped, elongated blotches of red, at first faint 
orange, upon the leaves and leaf sheaths, sometimes limited 
by the veins, and always more conspicuous on the inner 
than the outer sides. Smaller patches later blend into 
larger ones, and the affected parts die and finally turn black. 
The lower sides of diseased spots upon the leaves often 
bear red incrustations, resulting from the drying of the 
ooze from within. The roots show the same discoloration, 
and the outer parts of the rootlets die and become loose. 
If only slightly diseased, the plants may attain normal size. 

Badly diseased roots are evidenced by the yellowed tops 
and other signs of malnutrition. In advanced stages 
the roots give such poor anchorage that the plants may be 
easily pulled from the ground. 

Infected stalks should be burned and such rotation fol- 
lowed as to relieve the infected soil of susceptible crops for 
several years. 

Kernel smut (Sphacelotheca Sorghi (Lk.) Clinton). — 
This smut infests the individual grains of the panicle, 
while the head as a whole remains nearly normal in appear- 



CEREALS 



363 




ance. The smutted grains are at first covered by a white, 
later gray, membrane. This membrane in time becomes 
broken by the winter exposure and frees the dark-colored 
spores. 

The disease was reported by Kellerman in 1891 as limited 
to sorghum grown from imported seed. It was then known 
in District of 
Columbia, Wis- 
consin, New 
York, Nebraska, 
and Kansas. It 
is widespread in 
Europe, Africa, 
and Asia, and 
was probably im- 
ported into the 
United States 
upon diseased seed. It was first recorded in the United 
States in 1884, and is now found in almost all places where 
sorghum is grown. 

According to Clinton's estimates it may prevail upon 
from 4 to 32 per. cent of the plants. The same investigator 
found that the yield in juice was lessened about 30 per cent, 
owing to the smaller size of the smutted plants. 

As with oats, this smut can gain entrance to the host only 
during the very young seedling state, before the plants 
appear above ground. The mycelium of the causal fungus 
grows through the plant until flowering time without any 
symptoms of its presence. At blossoming time the fungus 
seeks the ovary, destroys it, and becomes evident as smut. 

Disinfection of the seed is an efficient remedy. The seed 



Fig. 158. — Three viewa of sorghum kernel smut. 
Original. 



364 DISEASES OF ECONOMIC PLANTS 

should be soaked in formalin, 1 pound to 30 gallons, for two 
hours, or sprayed with the same solution and piled over- 
night, as described for oats. The hot-water treatment, 
134° to 142 ° F. for 10 to 12 minutes, or the usual bluestone 
treatment, may be used if preferred. 1 

Head smut (Sphacelotheca Reiliana (Kuehn) Clinton). — 
Instead of involving the grains singly, as in the kernel 
smut, the head as a whole is affected. A white membrane is 
at first present, but this later breaks open, exposing the 
pulverulent spore mass. Rarely a portion only of the head 
is smutted. The spores soon weather away, leaving behind 
only the veins of the part involved. This disease was 
first noted in Egypt in 1868, and is known in abundance in 
America only in the Texas Panhandle. 

The treatments suggested for the kernel smut are of no 
avail in this case. The only remedy known is to avoid 
infected seed. 

Anthracnose (Colletotrichum falcatum Went.). — This was 
first found in America upon sorghum in North Carolina, 
where it did considerable damage. It has since been re- 
ported from Louisiana. It is worse upon the lower leaves. 
The spots have a very definite gray or tan-colored center 
which is surrounded by a dark, reddish brown ring, out- 
side of which is the ordinary green of the healthy leaf. 
As the spots age they frequently grow together and form 
one large oblong area, sometimes several centimeters long. 
At a late period in the development of the disease the 
centers of the spots are occupied by small black specks, 
the black acervuli of the causal fungus. 

1 Freeman, E. M., and Umberger, H. I. C, U.S. Dept. Agr. Bur. Plant 
Indus. Circ. 8, January 27, 1910. 



CEREALS 365 

TEOSINTE 

Smut. See corn. 
Rust. See corn. 

WHEAT 

Black stem rust (Puccinia graminis Pers.). — Though in 
earlier years this rust was thought to grow indiscriminately 
upon a great variety of grasses, recent thorough study 
has shown that what was formerly regarded as one species 
is in reality a number of races or varieties grouped under 
one name. The variety now under discussion is known to 
grow upon barley and wheat and upon several species of 
Elymus and Agropyrum and other genera of wild grasses. 

It is one of the most serious of the rusts, though fortunately 
not so universally present as the orange leaf rust, and causes 
more damage in the Central States than any other rust 
except the oat black stem rust. The damage done fluctuates 
largely. In some years it is very large, in others compara- 
tively slight. In 1904, a year of especially severe attack, 
the direct loss in yield was placed at 30,000,000 bushels in 
the Northwestern States, in addition to the loss in grade 
of the grain that was harvested. Total loss of the crop 
often results in Kentucky, Indiana, Texas, Michigan, and 
Ohio. 

Its spring or cluster-cup stage is upon the barberry, 
where swollen spots are produced upon the leaves, fruit, or 
young stems. These spots upon one side bear the cups in 
abundance and upon the other side appear as pale circular 
regions. 

Upon the wheat the rust shows first its uredosori, which 
come later than the uredosori of the orange leaf rust, and 



366 DISEASES OF ECONOMIC PLANTS 

are of more brownish tinge. The sori are most common 
upon the stems and leaf sheaths, more rare upon the leaf 
blade. As with some of the other cereal rusts, the uredo- 
spores may remain viable over winter, and thus perpetuate 
the rust, even without the aid of other forms of spores. 

Following upon this stage the black teleutosori appear 
upon the stems and leaf sheaths, constituting the most con- 
spicuous and predominating symptom. 

The damage by this disease is due to the inroads of the 
fungus upon the green leaf tissue, destroying the starch- 
producing power, diminishing the vigor of the plant, and 
showing its effects finally in the shrunken, shriveled grain. 

Since this rust usually appears late in the season, the 
varieties of wheat that mature early are likely to escape its 
attack to a greater extent than those varieties which are 
late in maturing. For a similar reason any climatic condi- 
tions which conduce to slow growth and late maturing of 
the crop favor the rust. Speaking of the resistance of the 
durum wheats, Carleton * says : — 

" Numerous reports indicate that the loss to the wheat 
crop by rust amounted to as much as 50 or 60 per cent over 
large areas in North Dakota, South Dakota, and Minnesota 
(in 1904), while in all cases the loss to durum wheat through 
the same source seldom reached more than 10 per cent, 
being usually 3 to 5 per cent, and sometimes nothing. Con- 
servative estimates have given the decrease in the entire 
production of wheat in the three states mentioned at from 
25,000,000 to 40,000,000 bushels, or a loss in the farm value 
of the wheat of at least $25,000,000. There is little doubt 
that if all wheat grown in these three states during 1904 had 

1 Carleton, M. A., U.S. Dept. Agr. Farmers' Bui. 219. 



CEREALS 367 

been durum wheat, this loss would have been entirely 
avoided." 

Orange leaf rust (Puccinia triticina Eriks.). — This is the 
most common and widely distributed of all rusts of the 
United States. It is said by Carleton that it is not only 
never absent from the wheat fields throughout the year, 
but that it is sometimes abundant even in dry seasons. 
Though it is so abundant, its inroads upon the crop are 
not usually serious, and in no case on record has it caused 
shriveling of the grain such as is common from the black 
stem rust. 

The most conspicuous feature of this rust is the abundant, 
orange-colored sori upon the leaves, especially upon their 
lower surfaces. The grayish black teleutosori are neither 
so prominent nor so abundant as in the black stem rust. 
Both of these rusts possess the uredo stage, and it is difficult 
for any but the expert to distinguish them apart in this 
condition. 

As with the rye orange leaf rust, this fungus also can winter 
its live uredo mycelium and continue to bear uredospores 
throughout the year, spending its entire existence, if neces- 
sary, in this one stage upon the single species of host. 

While no variety of wheat is entirely proof against it, 
large difference is shown in this respect, some varieties 
presenting high resistance, even under most adverse condi- 
tions. Early maturity is an important factor in evading 
rust. 

The following standard varieties are recommended by 
Carleton as possessing considerable resistance to the orange 
leaf rust in every part of the country — " Winter wheats : 
Turkey, Mennonite, Pringles No. 5, Rieti, Odessa, Pringles 



368 DISEASES OF ECONOMIC PLANTS 

Defiance. Spring wheats : Haynes Blue Stem, Saskatche- 
wan Fife. 

"The following varieties seem to be resistant, but have not 
yet been well established as such : Theiss, Oregon Club, 
Senora, Diehl Mediterranean, Fulcaster, Arnolds Hybrid,, 
California Spring. 

" Some of the hardy prolific sorts not yet well known in this 
country, but likely to be more or less rust-resistant after 
thorough acclimation and selection, are — Winter wheats : 
Prolifero, Banatka, Red Winter, Nashi, Tangarotto, Bearded 
Winter, Winter Ghirka, Budapest, Crimean, Yx, Bellevue, 
Talavera. Spring wheats: Alsace, Spring Ghirka. 

" Two varieties which are quite susceptible to rust, but 
which usually ripen early enough to escape the worst effects 
of it, are : Early May and Zimmerman. 

" Some others not quite so well known, but probably 
worthy of trial as rust-escaping sorts, are — Early Baart, 
Allora Spring, Kathia, Roseworthy, Japanese No. 2, Yemide, 
Canning Downs. 

" These last varieties are not likely to withstand very 
severe winters, and are therefore best adapted to southern 
districts, where they may perhaps in time become accli- 
mated. Yemide and Kathia are probably the most hardy 
of the six. Canning Downs winterkilled in one trial, even 
in Mississippi." 

Stinking smut (Tilletia foetans (B. & C.) Trek, Tilletia 
Tritici (Bjerk.) Wint.). — This smut (for practical pur- 
poses the two may be considered as one) is readily distin- 
guished from the loose smut by the fact that it attacks only 
the grain, not the inclosing chaff. The head therefore re- 
mains of much more nearly normal appearance, and it is 



CEREALS 369 

often not until the glumes have been opened, and their con- 
tents examined, that the presence of the smut mass is 
detected, covered with its membrane, and resembling the 
wheat grain in size and shape. It may be recognized by 
an expert observer by its peculiar, disagreeable, penetrating 
odor, and by the deeper green color of the diseased heads. 
The smut masses are often so firm as to remain unbroken 
through threshing, but they may be recognized among the 
grains by their darker color, greater plumpness, absence 
of groove and germ, and finally by crushing them and 
liberating the black spores. 

The disease is particularly destructive in that its presence 
signifies not only loss of grain due to replacement by smut, 
but also loss in value to the good wheat, which may be 
largely depreciated in price by the presence of the bunt. 
Often bunted wheat is worthless for milling purposes and 
even for cattle food. Bunt constitutes for these reasons 
one of the worst smuts in the world. Strong fanning re- 
moves part of the smutted grains, but troublesome wash- 
ing processes must be used to remove them all, and even 
then the results are not entirely satisfactory. 

Many smut spores naturally find lodgment upon the 
surfaces of healthy grains from smutted fields, or they may 
be carried from farm to farm upon the threshing machine. 
Upon planting such seed the following season these spores 
are ready to attack the seedling grain plant. The fungus, 
after gaining entrance into the seedling, grows with it 
throughout the season, and appears again at harvest time 
as spore masses within the chaff. Affected plants are 
usually smutted in every head and every grain in the 
head. 

2b 



STO DISEASES OF ECONOMIC PLANTS 

The seedling age, like that of the oat, is the only age sus- 
ceptible to smut infection. Treatment of seed wheat with 
formalin, as recommended for oats, is complete in its effi- 
ciency and trifling in cost. If formalin is not obtainable, 
immersion for twelve hours in one half per cent solution of 
copper sulphate (2 pounds to 50 gallons of water), then in 
milk of lime (2 pounds of lime to 20 gallons of water), for 
five minutes is recommended. The use of the lime cannot be 
omitted without endangering the germinating power of the 
seed. There is but little choice between these two treat- 
ments for wheat, though the formalin is perhaps safer in its 
effect upon the germinating power of the seed, especially if 
the lime is not used with the bluestone. The hot-water 
treatment, see p. 372, is serviceable but more laborious 
than either of the others. In any of these methods the 
seed must be dried, and the drill disinfected. See p. 346. 

Loose smut ( Ustilago Tritici (Pers.) Jens.). — Like the 
loose smut of barley, this smut seems to be increasing in 
importance. In some regions it prevails to a greater 
extent than the bunt, causing at times a loss of more 
than half the crop. It may be readily distinguished from 
stinking smut of wheat by the fact that the spore masses 
involve the whole spikelet, which becomes dry and powdery 
and falls away; also by its much earlier appearance in the 
field, i.e., at flowering time. The spore masses are dark, 
olive-black, and are produced exclusively in the spikelets. 
The bearded spring wheats seem to be more susceptible 
than the blue-stem varieties, but the smut is common on all 
varieties. 

From the studies of Maddox, 1896, in Tasmania, Wa- 
kagwa in Japan, Brefeld in Germany, and others, it is 



CEREALS 371 

known that with the loose smuts of wheat and barley, totally 
unlike the bunt of wheat and the loose smut of oats, infec- 
tion occurs exclusively at blossoming time; that at all other 
times the plants are immune. Smut spores from near-by 
smutted heads are blown into the wheat or barley flowers. 
Infection follows. The fungus then lies dormant in the 
grain until the seed sprouts. If the grain ripening from 
such infected flowers be used for seed, the fungus develops 
in the seedling, and an infected plant, producing smut but 
no grain, results, though no external symptom of the disease 
appears until blossoming time. Conversely, if seed result- 
ing from blossoms which were not infected be used, plants 
free from smut will be raised. 

The remedy in this case, therefore, lies in the use of unin- 
fected seed. To obtain such seed grain must be secured 
from a mother field in which there is no loose smut, or if 
this is not practicable, seed grain must be raised under such 
conditions as will afford clean seed. 

It has been found that while formalin, as a seed treat- 
ment, is ineffective against barley and wheat loose smuts, 
the Jensen hot-water treatment, in modified form, is effec- 
tive, and it could be used directly as a preventive, were 
it not that it is too difficult of manipulation to be appli- 
cable to large quantities, and that its use seriously en- 
dangers germination of the seed unless applied with great 
care. 

Rouging, or weeding out all diseased plants from the 
crop that is to be used for seed, diminishes the smut largely, 
but does not entirely eliminate it. 

A practicable, effective means, which results in complete 
and inexpensive eradication of this smut, consists of a com- 



372 DISEASES OF ECONOMIC PLANTS 

bination of the seed plat with the Jensen hot-water treat- 
ment. The directions for proceeding, drawn from Freeman 
and Johnson, 1 are as follows : — 

A good, clean, well-cultivated piece of land should be 
selected for raising seed. The plat should be large enough 
to provide at least twice as much grain as will be necessary 
for farm seed the following year in order to allow for loss 
in cleaning and selecting. This seed plat should not lie 
near fields of smutted crops of the same cereals, nor should 
it be so located that the prevailing winds at flowering time 
can carry spores to the seed plant from a neighboring field 
of the same grain. This isolation is absolutely necessary. 
A strip of wood, a cornfield, or a large meadow is a valuable 
protection. 

After seed for the plat has been cleaned by the best fan- 
ning and sifting, it must be treated by the Jensen method. 
The clean seed should be soaked for from five to seven hours 
in water at ordinary room temperature, 17° to 22° C. (63° 
to 72° F.), then placed in small, loose sacks or wire baskets, 
containing not more than one half peck each, and drained 
for a short time. The seed must be treated in small lots 
in order that all of the grain may quickly and uniformly 
reach the desired temperature. " Two tubs or vats of 
water should be provided. In one tub (No. 2) the exact 
temperature required should be maintained. The other 
tub (No. 1) is used for bringing the grain to the temperature 
of the treatment, so as not to lower the temperature in tub 
No. 2. Galvanized iron tubs of 20 to 40 gallons capacity, and 
kerosene or gasoline double-burner stoves, are convenient. 

1 Freeman, E. M., and Johnson, E. C, U.S. Dept. Agr. Bur. Plant Indus. 
152, July 12, 1909. 



CEREALS 



373 



The drained sacks or baskets of seed should be plunged into 
tub No. 1 for a minute, then transferred to tub No. 2, and 
kept agitated while immersed at temperatures and for the 
periods specified below, the temperatures mentioned being 



ColdO^ 
waterS-< 






water. 
Post. 



Fig. 159. — Diagram showing a convenient arrangement of utensils for the Jensen 
hot-water treatment. After Swingle. 



maintained as nearly as possible : For barley, 15 minutes 
at 52° C. (125.6° P.). For wheat, 10 minutes at 54° C. 
(129.2° F.). In treating barley, if the temperature should 
rise above 52° C. (125.6° F.), the time of immersion must 
be reduced to ten minutes at 53° C. (127.4° F.), or five min- 



374 DISEASES OF ECONOMIC PLANTS 

utes at 54° C. (129.2° F.). Above 54° C. (129.2° F.) 
there is no safe margin. If the temperature falls slightly 
below 52° C. (125.6° F.), the time of treatment should be 
increased in proportion. A temperature lower than 51 ° C. 
(123.8° F.) is not effective. In treating wheat, if the 
temperature should rise above 54° C. (129.2° F.) or fall 
below 52° C. (125.6° F.), the time for immersion must be 
diminished or increased accordingly. Under no circum- 
stances should a temperature of more than 55° C. (131 ° F.) 
be allowed. Temperatures below 51° C. (123.8° F.) are 
ineffective.' ' A reliable thermometer is necessary, since 
the use of an inaccurate instrument may result in injury to 
the germinating power of the grain or in failure to prevent 
the smut. 

Two men working together can easily treat one bushel 
of grain an hour, or enough seed in one day to sow a seed 
plat of from 6 to 10 acres. The seed may be dried by 
spreading it out in thin layers not over 5 cm. in depth 
on a clean granary floor or on canvas, and shoveling or 
raking it from time to time. It should not be allowed to 
sprout. Care must be taken to prevent freezing of the 
grain when it is moist, as this will impair germination. 

Seed treated as indicated may be planted as soon as it is 
sufficiently dry to run freely through the drills, making al- 
lowance for the swollen seed. Before sowing, the seed 
should be tested for germinating power, and a correspond- 
ing increase in the rate of seeding be made. 

The seed plat may be maintained from year to year, or as 
long as any smut is present in the grain fields. Seed ob- 
tained from the treated seed plat does not have to be treated 
the following year. 



CEREALS 375 

Anthracnose (Colletotrichum cereale Manns). — This an- 
thracnose seems to prevail on wheat as extensively as 
upon rye. Upon wheat the head or parts of it are not 
destroyed, as in the case of rye, but general weakness of 
the plant and light shriveled grain follows the attack. 

Powdery mildew (Erysiphe graminis DC). — The usual 
characters of the powdery mildews are exhibited : a whitish, 




Fig. 160. — Normal wheat kernels and shriveled kernels due to anthracnose. 
After Manns. 

flour-like coating in irregular circular spots upon the leaves 
and other plant parts. This mildew, together with the 
mildew of oats, rye, and barley, bears the same specific 
name, but upon each of these crops the form is so special- 
ized as not to transfer readily, if at all, to the other crop 
plant. Thus from the plant disease viewpoint there are 
practically four distinct kinds of mildew, although indistin- 
guishable to the eye. The form upon wheat grows upon all 
species of Triticum. 

In damp, shaded spots the mildew is sometimes quite 
injurious, though it is rarely so over any considerable 
area. The conditions favoring the disease should be 
avoided. 



376 DISEASES OF ECONOMIC PLANTS 

Leptosphaeriose (Leptosphceria tritici Pass.). — In Ne- 
braska, Heald 1 reported a disease in which the lower 
leaves were killed early in the season, and the whole field 
was pale in color. The loss was not large. 

Septoriose (Septoriasp.). — Septoriose has been noted by 
Selby 2 as small, dark spots upon the chaff of certain 
varieties of wheat. No damage was mentioned. 




Fig. 161. — Wheat kernels; a, normal; b, shrunken and killed by scab. After 

Manns. 

Scab (Gibberella Saubinetii (Mont.) Sacc). — This scab, 
first described in 1884 in England, seems to be quite gen- 
erally distributed in America, and is sometimes, though 
not usually, the cause of considerable loss. Under condi- 
tions favorable to the disease the loss may reach 10 per cent. 
It appears only upon the heads when about half ripe, as yel- 
low or pink incrustations on the spikelets, on the bases of 
the glumes, or covering the rachis. The affected spikelets 
ripen prematurely and turn yellow before the normal parts 

1 Heald, F. D., Neb. Agr. Exp. Sta. Rpt. 19, 46, 1906. 

2 Selby, A. D., Ohio Agr. Exp. Sta. Bui. 97, December 1898. 



FOB AGE CROP 8 377 

do. After ripening of the head, the diseased parts appear 
shrunken. The grain itself is hollow, shrunken, covered 
with a thick-felted mycelium, and is incapable of germi- 
nation. 

Only a few spikelets upon the head may be affected, these 
occupying any position, — basal, terminal, or intermediate, 
— or the whole head may be diseased. The loss occurs in 
injury to the quality of the grain and diminution in quan- 
tity. 

Selby has recently shown that seedlings in the field are 
often killed by this disease, which is carried over in the seed. 
In this way as high as 5.9 per cent of death in seedlings has 
been caused, and it is doubtless chiefly in this manner that 
the fungus is carried from crop to crop. 



FORAGE CROPS 
ALFALFA 

Leaf spot (Pseudopeziza Medicaginis (Lib.). Sacc). — 
No other disease of alfalfa is so widely, even universally, 
present as is this leaf spot. It constitutes the most impor- 
tant, in most sections the only really important, disease of 
this crop. It seems to be always, everywhere, under all 
conditions, present to some extent, and it often becomes of 
serious importance through the decrease in vigor which it 
causes, and by the loss in hay brought about by the shedding 
of the leaves. Pammel in Iowa in 1891 estimated the loss 
in some fields at 50 per cent. It was first described in 
Europe in 1832, and noted in the United States in 1875. 

The leaves first show small brown to black spots, irregular 
or circular, which extend through the leaf and are thus 



378 



DISEASES OF ECONOMIC PLANTS 



visible from both sides. They are about 1-2 mm. in di- 
ameter, and are not sharply bordered, but shade off grad- 
ually into the surrounding tissue. With a hand lens very 
small, spore-bearing organs may be seen in the centers of 
the older spots, first as shiny amber-colored elevations. 
These elevations soon crack open and expose very small, 



4&W- 



Fig. 162. — Four alfalfa leaf spots ; 1, ascochytose ; 2, pseudopezizose ; 3, cercos- 
porose; 4, stagonosporose. After Stewart and others. 

disk or cup shaped sporiferous bodies, which remain sur- 
rounded by portions of the ruptured epidermis. Badly 
diseased leaves usually turn yellow and fall off. Spots 
upon the stems show the same general character as those 
upon the leaves. 

The lower leaves, and the leaves of older plants, are most 
subject to the leaf spot. Plants late in the season, as of 
the second and third cuttings, suffer much more than earlier 
in the season. These crops, especially if allowed to stand 
a little too long before cutting in a dry season, may be badly 



FOB AGE CROPS 379 

spotted, and the loss in hay, through falling of the leaves, 
may be considerable. The vigor of the plants is also seri- 
ously impaired, both by the loss of green tissue of the leaves 
that persist, and by the loss of leaves that fall. The plants 
are never killed by this disease, though young fields which 
have not yet become well established may be ruined. 

The leaf spot attacks yellow trefoil, and a disease which 
is perhaps identical with it is found upon red clover. 

Its mode of dissemination is unknown, but infection 
through seed is probabfy one method. Notwithstanding 
this fact, seed treatment would probably be without avail 
as a preventive. 

The only practicable treatment is to mow down badly 
diseased plants with the hope that the new shoots which 
spring forth may overcome the disease. If the disease 
appears just before cutting time, the mowing should be 
hastened a few days in order to avoid loss from leaf sheddingo 

Sclerotiniose, wilt (Sclerotinia Trifoliorum Eriks.). — 
This wilt, which in some respects resembles lettuce 
sclerotiniose and which may be caused by the same fungus 
which causes that disease, has been noted in several widely 
separated sections of the United States. 

It kills the plants, and under favorable weather conditions, 
the chief factor of which is a humid atmosphere, it may ex- 
tend from plant to plant and cause large sick areas in the 
field. 

Sick plants may show a variety of symptoms. Some- 
times the leaves droop, and become matted together in a 
sodden mass at the base of the plant, and overgrown with 
a white cotton-like mass of mycelium, in which black scle- 
rotia, similar to those described under lettuce, are found. 



380 DISEASES OF ECONOMIC PLANTS 

At other times the stems may be the point of attack, show- 
ing dead brown sections covered with the mycelium and 
bearing sclerotia. Upon splitting a stem open the central 
part may be found full of mycelium and with occasional 
sclerotia about the size of a grain of wheat. The white 
mycelium and sclerotia are absolutely diagnostic. 

Under unfavorable weather conditions the disease may 
die out and fail to reappear, but if the weather is favorable 
to it, the wilt may reappear year after year with increased 
vigor and involving larger and larger areas. 

Stewart, French, and Wilson 1 reported large areas where 
50 per cent of the stalks were killed, though later the field 
recovered entirely. 

If the disease becomes troublesome, rotation of crops 
seems to be the only recourse. 

Root rot, wilt, fusariose (Fusarium sp.). — The first 
sympton of this wilt is a yellowing of the outer leaves which 
gradually spreads until all of the leaves and stems become 
discolored, wilt, and die. This rot is said to be quite gen- 
erally destructive in Arizona. It is a soil disease, and its 
general characters are those indicated on p. 63. 

Root rot, rhizoctoniose (Rhizoctonia Medicaginis DC). — 
Similar to the effects of rhizoctoniose upon so many 
other hosts, the disease consists primarily of a root rot in 
which the diseased parts are coated with matted strands 
of the fungous mycelium, usually brownish red or violet 
in color, accompanied by sclerotia. The tops of plants so 
diseased turn yellow and die. 

The very aggressive fungus migrates through or over the 

i Stewart, F. G, French, G. T., and Wilson, J. K., N.Y. (Geneva) Agr. 
Exp. Sta. Bui. 305, November, 1908. 



FOB AGE CHOPS 381 

soil to adjoining plants, and the affected spot in the field 
thus enlarges, sometimes at a rate of 7 m. radially per year. 
Though long known in Europe, it has not yet appeared in 
many parts of America. 

Rhizoctoniose is a typical soil disease and is kept alive 
in the soil by its sclerotia, which may live at least two or 
three years. The general suggestions given under soil dis- 
eases apply. 

Texas root rot (Ozonium omnivorum Shear.). — This rot is 
the same that affects the cotton so disastrously, and which is 
discussed fully under cotton diseases. It is a soil disease 
which in its general characters is the same as those shown 
upon cotton, and the treatment applied to cotton is the 
only one to be recommended for alfalfa. It has been very 
destructive in Texas since 1892. 

Anthracnose (Colletotrichum Trifolii Bain). — Alfalfa 
anthracnose was first mentioned in 1905 x by Bain and 
Essary, who stated that it was abundant in Tennessee 
in 1906 and was one of the chief causes of alfalfa failures in 
that state. It has also been noted in destructive form in 
Virginia and New York. It appears as elliptical, sunken 
spots, 5-6 mm. long, upon the stems. The spots are gray 
and have dark acervuli scattered over them. Where the 
disease becomes aggressive, dead or withered stalks or 
plants are seen scattered over the field. These stalks arise 
from diseased crowns, which are characterized by blacken- 
ing of the woody parts, below the point where the diseased 
stalks are attacked. The only remedy seems to be the use 
of resistant varieties. 

Ascochytose (Ascochyta Medicaginis Bres.). — This leaf 

1 Bain, S. McC., and Essary, S. H., Sci. n. s. 22, 503, October 20, 1905. 



382 DISEASES OF ECONOMIC PLANTS 

spot has been noted in North Carolina, and what is 
probably the same disease, also in New York. 

The spots are irregularly circular except where they occur 
on the edge of the leaf, light brown in color, and bear small 
black dots. The disease is not important. 

Cercosporose (Cercospora Medicaginis Ell. & Ev.). — This 
disease appeared in Delaware in 1889 and has also been 
noted in New York and New Jersey. 

The leaf spots are nearly circular, smoky brown to black, 
from 0.5-1 mm. in diameter, and show equally well from 
either surface of the leaf. They have no well-defined bor- 
ders, but shade into the surrounding healthy tissue. Af- 
fected leaves turn yellow and die. 

Pseudomonose (Pseudomonas Medicaginis Sackett). — 
From Colorado Paddock, 1 in 1906, described a severe dis- 
ease of alfalfa which has been noted for several successive 
years. 

It is due to bacteria 2 and in its early stages produces a 
watery, semitransparent, yellowish to olive-green appear- 
ance along one side of the stem of the plant. The plants 
are at first weak, and light colored, then discolored or black- 
ened on the stems. Drops of thick fluid ooze from the 
stems and dry upon them, giving a glistening appearance as 
if they were varnished. The chief damage is to the first 
cutting, though in subsequent years the plants may die 
from decay of the crown, or roots, or from loss of nutrition. 
Infection seems to be chiefly through rifts in the epider- 
mis due to frost, and is caused by wind-borne bacteria. 

1 Paddock, W., Col. Agr. Exp. Sta. Press Bui. 28, November, 1906. 

2 Sackett, W. G., Soc. Am. Bact., Boston meeting, December, 1909. 
Also Colo. Agr. Exp. Sta. B. 158, 1910. 



FORAGE CROPS 383 

Downy mildew (Peronospora Trifoliorum DeBy.). — 
Downy mildew, which is a serious pest in Europe, has 
been reported in America from Colorado, Kansas, New 
York, and North Carolina, though it has not yet been de- 
structive in this country. The affected parts of the leaf 
turn yellowish gray to purple, and are frequently curled. 
The leaves, as seen from below, are coated with the downy 
fuzz, violet when old, characteristic of this class of diseases. 

Rust (Uromyces striatus Schroet.). — The true rust of 
alfalfa may be recognized by the typical rust sori, which 
are, in this case, chiefly upon the lower sides of the 
leaves. It is not usually serious. 

Gloeosporiose (Glceosporium Medicaginis Ell. & Kell.). — 
Black, rather prominent acervuli appear chiefly upon the 
lower surfaces of leaf spots. The lower leaves often turn 
yellow and die. 

Seed mold (Alternaria sp.). — Brown, dead, shriveled 
seeds are often noted in samples of alfalfa seed. Such 
seeds, if planted, develop, apparently from within, a dense 
black mold due to a species of alternaria. 

The economic importance of this condition is not known. 

Damping off (Rhizoctonia sp. and Pythium DeBaryanum 
Hesse) . — The damping off of alfalfa is chiefly caused 
by the two fungi above named. Damping off is discussed 
in general on p. 60. 

It has been known to affect alfalfa seedlings in the green- 
house, and it may occur to some extent in the field, especially 
the form caused by rhizoctonia. 

Stagonosporose (Stagonospora carpathica Baeuml.). — 
This in no case destructive leaf spot has been noted only 
in New York, and is described as follows by Stewart, 



384 DISEASES OF ECONOMIC PLANTS 




Fig. 163. — Alfalfa plant and dodder. After Stewart and others. 



French and Wilson * : Unlike the ascochyta leaf spot, this 
disease attacks chiefly green leaves in the upper part of 
the plant. The spots are circular, 1-3 mm. in diameter, 
and usually light brown with a narrow border of dark 

1 Stewart, French and Wilson, I.e. 



FORAGE CROPS 



385 



brown. Each spot bears several light brown pycnidia 
visible on both surfaces of the leaf. 

Dodder (Cuscuta). — Dodder, or love vine, is a parasitic 
flowering plant. It consists of yellow, threadlike stems 
which coil closely around the alfalfa stems, and take nour- 
ishment from them. It reproduces by seed, and the seed 
may readily pass with alfalfa seed unless very carefully in- 






1 2 3 

Fig. 164. — 1, Alfalfa seed ; 2, seed of large seeded dodder ; 
3, seed of small seeded dodder, natural size. After Stew- 
art and others. 

spected. The parasite is absolutely ruinous to the portions 
of the field that are infected by it, and, since it spreads 
rapidly, it is a very serious enemy. 

Badly infected fields should be plowed up. If fields are 
infected in only a few spots, these spots may be dug over or 
burned over before the dodder ripens its seed, using kero- 
sene and straw to insure heat sufficient to kill every in- 
fected plant, and a margin of a few feet entirely around the 
infected spot. 

BLUEGRASS 

Rust (Puccinia Poarum Niels). — The uredo of this 
rust takes even greater prominence than does the uredo of 
2c 



386 



DISEASES OF ECONOMIC PLANTS 



most other rusts ; indeed other forms of spores are almost 
entirely absent in most parts of the country, throwing the 
burden of perpetuation of the species entirely upon the uredo 
mycelium and its spores. This stage is known to be peren- 
nial as far north as Washington, DC, and Lincoln, Neb. 
The rust is very destructive, and seems to be limited to 

this one host. 

Smut. See timothy. 
Anthracnose. See 
rye. 

CLOVER 

Black mold (Phyl- 
lachora Trifolii 
(Pers.) Fckl.).— 
Common red clover, 
crimson clover, white 
clover, alsike clover, 
and several other related plants are affected by this mold. 
The chief symptoms are pale spots upon the upper sides 
of the leaves accompanied by black dots on the lower sides. 
These spots at first glance so strongly resemble the sori of 
the rusts as to lead the disease to be mistaken for a rust by 
the casual observer. 

Though the disease is often of considerable damage, no 
treatment is known. 

Sclerotiniose, wilt (Sclerotinia TrifoliorumEriks.). — This 
wilt is possibly identical with the wilt of alfalfa. In any 
event it resembles it very closely. It was first noted 
in America, in Delaware, by Chester in 1889, later in New 
Jersey by Halsted. 




Fig. 165. — Clover leaf showing spots of black mold. 
Original. 



FORAGE CROPS 387 

The affected plants wilt and rot to the ground, and white 
mats of mycelial threads, and later black sclerotia, are 
found upon or within the dead stems. Sclerotia are es- 
pecially abundant at the bases of the sick stems. Disk- 
like bodies, similar to those described in connection with 
lettuce sclerotiniose, develop from the sclerotium and bear 
spores which spread the infection. 

While this malady has been very destructive in Europe 
upon several varieties of clover, it has not yet attained 
wide distribution in America, though it has appeared in a 
serious way in a few fields. 

It is exceedingly difficult to eradicate when it has once 
gained foothold, and the European recommendation is to 
avoid planting the affected fields to susceptible crops. 

Rust (Uromyces Trifolii (Hedw. f.) Lev.). — The clover 
rust is most injurious to the second crop, to which it may 
cause a damage of 20 per cent or even 50 per cent if con- 
ditions favorable to the disease — damp, cool weather — 
obtain. 

This rust, long known in Europe, whence it is probably 
adventive, was first reported in America in 1884. At the 
present time it is found upon red, white, crimson, and 
alsike clovers over a large part of the United States. 

It is one of the true rusts, and on the white clover pos- 
sesses all of the three stages, cluster cup, summer or uredo, 
and winter or teleuto spores. It attacks all green parts of 
the plant. The most conspicuous and destructive stage 
is the uredo, which is marked by an abundance of circular 
or elongated chestnut-brown powdery sori. These may be 
few and scattered, but more often they are quite abundant, 
nearly covering the leaf. If abundant, the leaf turns black, 



388 



DISEASES OF ECONOMIC PLANTS 



dies, and shrivels. The rust is conveyed from plant to 
plant throughout the summer by spores of this stage. 

The teleutospores may appear in the same sori with the 
uredospores or in separate sori, and in either event come 




Fig. 166. — Clover leaf showing sori of rust. Original. 



later in the season. They are recognized by their darker 
brown color. The cluster-cup stage, which is less abun- 
dant and less injurious than the other stages, may often 
pass unnoticed. It appears first as pale swollen regions 
upon the leaf or petiole. These regions soon show the 
characteristic cups with orange-colored spores. The cluster- 
cup stage, though not known on red clover, predominates 



FORAGE CROPS 



389 



in the early spring, upon many other varieties; but the 
uredo stage soon gains the ascendancy over it. All three 
forms may be produced side by side, to some extent, 
throughout the summer. 

Hibernation probably occurs in two ways, by the teleu- 
tospores and by the mycelium, 
which may remain alive in the 
affected parts over winter. 

Anthracnose (Cottetotrichum 
Trifolii Bain). — This anthrac- 
nose is now known in Ten- 
nessee, Ohio, West Virginia, 
Arkansas, Kentucky, and Dela- 
ware. It is first found chiefly 
upon the leaf stalks, later upon 
the stems, near the surface of 
the ground and just below the 
flower clusters, as elongated 
sunken spots, which result 
eventually in the death of the 
whole plant. It frequently 
causes great loss, and is said 
by Bain to be the most serious 
plant disease in Tennessee. 
The same disease occurs upon 

alfalfa, but alsike clover is nearly immune. The greatest 
hope lies in the breeding of resistant varieties. 

Anthracnose (Gloeosporium caulivorum Kirchner). — 
Long, brown to black, sunken spots upon stems and petioles, 
causing death of the more distal parts, are diagnostic 
characters of this anthracnose, which was first reported in 




Fig. 167. — Anthracnose on red 
clover stem and petiole. After 
Jackson. 



390 DISEASES OF ECONOMIC PLANTS 

the United States by Sheldon in 1906, and has since been 
noted as serious in a number of states. 

Leaf spot (Pseudopeziza Trifolii (Biv. Bernh.) Fckl.). — 
Perhaps identical with the similar disease of alfalfa, this 
occasionally causes considerably damage. 

Macrosporiose (Macrosporium sarciniceforme Cav.). — 
This widely distributed black mold is a common cause of 
leaf spots. 

Scab (Gibberella Saubinetii (Mont.) Sacc). — This 
parasite of grains is also known to cause depressed oblong 
spots upon clover. See wheat. 

Broom rape (Orobanche minor. L.). — The parasite which 
causes this disease is very similar to that upon tobacco. 
See p. 307. Orobanche has also been noted upon pelar- 
gonium, tomato, coleus, and several other plants. 

Dodder. See alfalfa. 

CRAB GRASS 

Piriculariose (PiriculariaOryzce Cav.). — This is proba- 
bly identical with rice blast. See p. 352. 

COWPEA 

Wilt,fusariose (Fusarium vasinfectum Atk.) — This disease 
is closely like fusariose of cotton, okra, and watermelon, 
though the disease is not communicable from one of these 
plants to the other. 

It first appears when the plants are about six weeks old. 1 
Up to this time they will grow well and appear healthy. 
Scattered plants then begin to drop their leaves, the lower 
ones falling first. Growth is checked, and the stem shows 

1 Orton, W. A., U.S. Dept. Agr. Bur. Plant Indus. Bui. 17, April, 1902, 



FORAGE CROPS 



391 



a faint reddish brown tinge. After the leaves have fallen 
the stem dies and becomes covered with a light pink coat- 
ing of the spores of the wilt fungus. The spread of the 
disease is more gradual 
and less conspicuous in 
the early part of the 
season, but after the peas 
begin to set fruit they 
succumb rapidly, and a 
field that in July may 
promise a fine crop may 
be entirely dead before 
September without hav- 
ing matured a pod. The 
disease usually appears in 
spots, like the cotton wilt, 
and these diseased areas 
spread until they may 
cover a whole field. 

In moderate cases, or 
where the varieties planted 
are less subject to the 
disease, only the weaker 
plants are killed, while 
the rest are dwarfed and 

their yield reduced. Careful examination of the roots 
shows that many of the small lateral roots are dead, small 
tufts of roots marking the points of infection. Fig. 168. 
This tufting of the rootlets is similar to that produced on 
cotton by the cotton wilt fungus. 

In all cases the veins of the stem are brown, and the dis- 




Fig. 168. — Roots of diseased cowpea at 
left ; healthy roots on the right. After 
Orton. 



FORAGE CROPS 



393 



ease may be clearly distinguished by cutting across the stem 
and observing whether the color of the wood is normal. 
This discoloration, which may often be seen through the 
translucent stem of the cowpea, is characteristic of this 
class of diseases. The name " wilt " is somewhat mislead- 




Fig. 170. — Cowpea leaf spot (amerosporiose). Original. 

ing, as the leaves usually drop off before there is any con- 
spicuous wilting. 

The causal fungus is carried by the plow and cultivator, 
as evidenced by the spread of the disease lengthwise of a 
field, and by cattle, in cases where they pass through an in- 
fected field on their way to pasture. It may also be car- 
ried by drainage water, and by other of the ways suggested 
under soil diseases. The disease is now known in most of 



394 



DISEASES OF ECONOMIC PLANTS 







the Southern States from North Carolina to Florida, and 
west to Texas, and is yearly noted in new localities. 

Owing to the all-important position the cowpea occupies 
in southern agriculture as a nitrogen crop, where the best 

rotation demands its 
frequent recurrence 
upon the same soil, the 
disease is of peculiar 
moment. 

No remedy is known 
except the use of the 
iron cowpea, the re- 
sistance of which was 
/" ^f| . : W noted by Mr. T. S. 

^ ' '■■"■'Sr Williams of South Car- 

^*«8 ., ./*^r olina in 1900, and fur- 

^^^^^ ther tested by W. A. 

Orton of the United 
States Department of 
Agriculture. 

Leaf spot (Amerosporiwn ceconomicum Ell. & Tracy). 
— This disease is readily distinguished from cercosporose 
by the fact that the spots are circular, are of shiny white- 
ness, and are studded all over with little black pycnidia, 
smaller than an ordinary pinhole. Fig. 170. The disease is 
often abundant, but is usually not so serious as cercos- 
porose. 

Powdery mildew (Erysiphe polygoni DC). — The white 
spots of this mildew are strictly circular when young, but 
as they enlarge they coalesce and cover the whole upper 
surface of the leaves with a white powder. 



Fig. 171. — Cowpea leaflet spotted wlta pow- 
dery mildew. Original. 



FORAGE CROPS 



395 



The disease is very widespread, but even in the worst 
seasons does not do much 
injury. 

Angular leaf spot (Cer- 
cospora cruenta Sacc). — 
The angular leaf spots of 
this disease are a famil- 
iar sight in most cowpea 
fields. They are of vari- 
ous colors above, chiefly 
reddish, and are gray to 
purplish or slate-colored 
below. 

The damage is rarely 
very great. In some in- 
stances the attack may 
proceed to the stems, 
where, especially at the 
base, it may cause crack- 
ing and result in such 
lowering of the vigor of 
the plant as to cause 
shedding of leaves and 

failure to properly fill the pods. The loss of leaves is of 
course serious to the hay value of the crop. 

JAPAN CLOVER 

Powdery mildew {Microsyhcera diffusa C. & Peck). — 
The usual characters of the powdery mildews distinguish 
this disease sufficiently. The injury to this valuable 
southern forage plant, while considerable, is never suffi- 
cient to call for treatment. 




Fig. 172. — Leaflet of cowpea showing cer- 
cosporose spots. Original. 



396 DISEASES OF ECONOMIC PLANTS 

ORCHARD GRASS 

Scolecotrichose (Scolecotrichum graminis, FckL). — In 
times of severe drought elongated dead spots may 
appear upon orchard grass, most conspicuous upon the 
lower outer leaves. Following these comes the death of 
the leaf, sometimes starting at the leaf tips and reaching 
to the base. In conditions favorable to the disease whole 
plants are involved. The spots, before they become con- 
fluent, are of quite characteristic appearance: large, dark 
brown to purplish brown. When old, they usually show 
at their centers spots of gray or white, and these spots 
may be marked with very small black pycnidia arranged 
in rows lengthwise of the leaf. 

Black stem rust (Puccinia graminis Pers.). — This rust is 
identical with the oat rust caused by Puccinia graminis, and 
it may be conveyed from either of these hosts to the other. 

Rust (Puccinia Rhamni (Pers.). Wett.). — It is probable 
that orchard grass can act as host for this species, which 
has been described under oats. 

Anthracnose. See rye. 

QUACK GRASS 

Smut. See timothy. 

Smut, urocystose ( Urocystis Agropyri (Preuss.) Schroet.). 
— This smut resembles the above closely in the general 
appearance of its sori, though microscopically its charac- 
ters are quite different ; its spores show a more reddish hue. 

RED TOP 

Black stem rust (Puccinia graminis, Pers.). — The rust 
is identical with that upon wheat and oats, though in- 
fection does not readily occur from one host to the other. 



FORAGE CROPS 397 

Smut (Ustilago strimformis (Westend.) Niessl.). — This 
is the smut described under timothy. It has been known 
to affect 30 per cent of the plants, and to reduce the seed 
yield from 300 hundredweight to 70 hundredweight. 

Anthracnose. See rye. 

TALL OAT GRASS 

Smut {Ustilago perennans Rostr.). — This smut closely 
resembles that of oats, though the flower parts are not 
so completely destroyed as is the case in oat smut. The 
disease is perennial in its perennial host, and smutted plants 
bear smut, year after year. 

TIMOTHY 

Smut (Ustilago striaformis (Westend.) Niessl.). — This 
smut occurs chiefly upon the leaves, more rarely upon 
other parts of timothy, as well as upon some species of 
Agrostis, Poa, and Elymus. The spore masses form long 
black lines upon the leaf, and by merging and rupturing 
reduce the leaf to a torn, blackened state. The affected 
plants are weakened, small, and often fail to make seed. 
The disease perenniates with the host. Infection proba- 
bly occurs through the seed. 

Rust (Puccinia graminis Pers.). — This rust in general 
resembles the black rust of the grains. It was first 
reported in 1882 and has of recent years increased rapidly. 
It does not seem to be communicable to other grasses. 

Anthracnose. See rye. 

VETCH 

Spot (Protocoronospora nigricans Atk. & Edg.). — Upon 
the stems, leaves, and bracts of vetch very characteristic, 



398 DISEASES OF ECONOMIC PLANTS 

long, narrow, or elliptical spots are formed, frequently 
with a dull, purple border, and usually with a white 
center. When on the pods, they are obliquely situated. 
When old, they appear as black, oblique lines. 
No serious damage has been reported. 



FIBER PLANTS 
COTTON 

Wilt, fusariose (Fusarium vasinfedum Atk.). — The cot- 
ton wilt, now widely distributed and yearly preempting 
more territory, is caused by a fungus that plugs the water 
ducts in the veins of the stem and cuts off the water 
supply to the parts above, always reducing the vigor of the 
plants and usually resulting in speedy death. 

Soil which produces a sick crop one year is so infested 
with the causal fungus as to insure reappearance of the 
disease in more extensive areas in subsequent croppings 
with the susceptible plant. The destruction of this form 
of disease, which takes not only the crop, but in part the 
usefulness of the soil as well, cannot be estimated. Its 
injury can only be realized by those who have experienced 
its effects. 

Wilt has long been known by southern cotton planters, 
and is now prevalent in many sections of Alabama, Arkan- 
sas, North Carolina, South Carolina, Georgia, Louisiana, 
and probably throughout the whole cotton belt. Many 
foreign countries also record it. 

The first appearance of the wilt is a yellowing of the 
lower leaves at the edges or between the main ribs, which 
portions may become almost white ; later they turn brown 



FIBER PLANTS 



399 



and die. A single leaf often presents the three conditions, 
green (healthy), yellow (sick), and brown (dead), side by 
side in bands, parallel to the main ribs and radiating from 
the leaf stem. The dead parts may break away, leav- 
ing the leaf ragged. The upper leaves follow rapidly over 
the course of the lower leaves. The leaves as soon as badly 
affected fall away, leaving only a bare stalk. In mild cases, 




Fig. 173. 



A variety of cotton resistant to the wilt ; note the complete failure of 
the other varieties. After Orton. 



where the disease runs its course more slowly, the intervals 
between the different stages are more prolonged. In light 
sand the disease may progress very rapidly and may con- 
sist of only two stages, the sudden wilted condition followed 
by speedy death. The final diagnostic symptom of the dis- 
ease, however, as in the case of many other wilts, is the 
darkening of the affected veins, which change from the 
normal white to light brown or black. Though in most 
cases the plant dies, occasionally one revives and seems to 



400 DISEASES OF ECONOMIC PLANTS 

outgrow the disease. In such plants relapses may follow, 
showing somewhat different symptoms, among them decay 
of the boll, and a different sequence of color changes. 

Rotation of crops should be practiced and the diseased 
plants should be pulled and burned to check the spread of 
the disease in the soil, and in general the recommendations 
given under soil diseases should be followed. The ultimate 
solution of the question must be in the employment of 
resistant varieties. One such, a long-staple cotton, has 
been bred up by the United States Department of Agricul- 
ture. 

Anthracnose (Glomerella gossypii (South.) Edg.). — The 
causal fungus of this disease was first described in 1890. 
The disease is very destructive in some localities and pre- 
vails throughout a large portion of the cotton belt. In cen- 
tral Georgia it is said to destroy about 22 per cent of the 
crop yearly, sometimes more ; while to the state as a whole 
the loss is put at 17 per cent or approximately $14,750,000. 

It is most conspicuous upon the bolls, where it produces 
unsightly ulcers, at first black, and later bearing a coat of 
pink. The ulcers have dark brown to black, watery borders 
and vary in diameter from a few millimeters to covering 
the whole boll. When small, the spots are reddish and 
slightly depressed. Attacks upon young bolls stop their 
growth and induce premature ripening and imperfect open- 
ing, or the bolls may die and decay without opening at all. 
In such bolls the fungus is found upon the lint and seed 
within. Upon the stems the fungus is limited mainly to 
injured parts, leaf scars, etc., and to very young, tender 
plants, causing damping off. Here it is accompanied by 
reddening and by shrinkage in longitudinal lines. This 



FIBER PLANTS 401 

disease upon young plants usually follows the use of dis- 
eased seed. Upon old stems it causes blighting of the 
bark, which becomes reddish brown and dies. 

Upon the leaves as upon the stems the attack is mainly 
limited to injured or weak parts. The seed leaves, being 
in a state of weakness, are especially susceptible to the 
fungus, which develops here with characters very similar 
to those of the stem and the boll. The leaves sometimes 
have a scalded look, assume a yellowish or leaden green 
color, and wither and die, much as though frosted. 

There is abundant evidence that the disease is largely 
carried from year to year in the seed. Therefore, only seed 
from entirely healthy fields and seed that has been ginned 
where only healthy cotton has been ginned should be used. 
No mode of seed treatment has proved reliable. 

Texas root rot (Ozonium omnivorum Shear.). — The first 
technical description of this disease was given by Pammel 
in 1888. It has since been the subject of many papers, and 
is known to occur in very destructive form in Texas, Okla- 
homa, New Mexico, and Arizona, though it has not yet 
been found east of Texas. 1 The estimated loss from 
ozoniose in 1906 in Texas was about $3,000,000. Some 
planters regard it as a worse enemy than the boll weevil. 

In this disease a few of the plants may wilt and dry up 
in a day. This usually occurs at or before blossoming, 
occasionally upon plants only a few inches high. Later, 
many plants suffer similar fate, resulting in irregular spots 
of disease in the field, marked by the presence of numerous 
standing, dead plants. The plants succumb with especial 

1 Shear, C. L., and Miles, Geo. F., U.S. Dept. Agr. Bur. Plant Indus. 
Bui. 102, Part V, September 9, 1907. 
2d 



402 DISEASES OF ECONOMIC PLANTS 

rapidity on hot days following rain, not so rapidly in con- 
tinuous dry weather. Especially after a rain, living plants 
surrounded by dead ones may show S3nnptoms of the 
disease in the form of dense sterile mycelium upon the tap 
root. All diseased plants have diseased roots marked by 
injured rootlets and shrunken tap roots, accompanied by 
depressed spots which are at first bordered by red dis- 
coloration. The causal fungus is also apparent here, at 
first as a white mold which later turns brown or yellow 
and is finally accompanied by wart-like sclerotia. En- 
largements, from which new roots are put forth, often 
occur near the soil surface. Even the lint of the diseased 
plants is affected, the fibers being wider and larger, and 
the spirals fewer and more uneven, than upon healthy 
plants. The disease is truly of the soil, and the diseased 
soil centers enlarge yearly as in other soil diseases. It 
is subject to the modes of dissemination suggested on 
page 65. 

Especial precautions should be exercised against the use, 
for the purpose of legume inoculation, of soil which may 
possibly be infested with the disease. This warning is 
particularly necessary in view of the fact that alfalfa is 
affected by the same disease, and the causal fungus is now 
present in many alfalfa fields. 

As to treatment, rotation with immune crops in con- 
junction with deep fall plowing is recommended. Shear 
and Miles * say: " Rotation with immune crops at Terrell, 
Tex., resulted as follows : 1904, planted to cotton, about 95 
per cent of which was killed by root rot ; 1905, planted to 

1 Shear, C. L., and Miles, Geo. F., U.S. Dept. Agr. Bur. Plant Indus. 
Circ. 9, June 19, 1908. 



FIBER PLANTS 403 

corn; 1906, planted to wheat, followed by sorghum the 
same season; 1907, cotton again planted, with the result 
that, as nearly as could be estimated, less than 5 per cent 
of the cotton was dead at the close of the season. 

" Land badly infected with the root rot was plowed seven 
to nine inches deep November 11, 1906, at Petty, Tex. In 
experiment No. 1 the deep-plowed plat showed 42.75 per 
cent less dead plants than the adjoining check plat which 
received the customary tillage. In experiment No. 2 the 
deep-plowed plat showed 43 per cent less dead plants than 
the adjoining check plat, and in both cases a much larger 
amount of cotton was produced on the dead plants on the 
treated plats, because these plants did not die until later 
than those on the untreated plats, and therefore had greater 
opportunity to mature their bolls." 

Frosty mildew (Ramularia areola Atk.). — This leaf spot 
is limited sharply by the smaller veins, and bears upon the 
lower surface numerous colorless spores upon colorless 
hyphse, thus lending a frosted appearance. Seen from 
above, the spots are light yellow or of a paler green than 
the normal leaf tissue. Widespread, though not especially 
destructive, it does not usually attract the attention of 
the planter. 

Leaf blight (Mycosphcerella gossypina Atk.). — The fun- 
gus which causes this disease was first described from 
Carolinian specimens in 1883, at which time its presence 
was recognized in South Carolina, Georgia, and Florida. 
The disease prevails in all cotton sections of the United 
States, appearing first in damp localities upon the lower 
leaves, and with the progress of the season spotting all the 
leaves more or less. The leaf spots appear at first as small 



404 DISEASES OF ECONOMIC PLANTS 

red dots, which finally, as they enlarge, bear brown or white 
centers with a characteristic red border. A copious de- 
velopment of dark hyphae jipon the centers later gives 
them a blackish hue, and an abundance of white spores gives 
these hyphse a white coating. The old diseased centers 
of the spots are brittle and frequently break away, leaving 
perforations. The disease is widespread but unimportant, 
since it is largely limited to weakened tissues, especially 
to spots produced by cotton mosaic. 

Bacteriose {Bacterium malvacearum E. F. Smith). — Wide- 
spread but seldom abundant enough to attract attention, the 
diseased areas appear as angular spots bounded by the veins 
and of a watery appearance. They may be scattered over 
the leaf, or they may be nearly contiguous and later 
become confluent, resulting in irregular dead patches. 
Frequently they are most numerous adjacent to the main 
ribs, and result in long, irregular, dead, black regions. 
The dead tissue is brittle and often falls away, causing 
holes or ragged edges. Badly affected leaves fall early. 

Boll rot. — This rot in wet seasons may cause the loss of 
nearly all of the crop. It sometimes begins as small, black 
or dark brown spots upon the young seed and lint, especially 
near the base of the boll, and thence invades the whole boll, 
showing itself externally only when nearly all of the inner 
part of the boll has decayed. If it begins later, only a few 
seeds and their lint may rot, and the remainder of the boll 
may ripen and be harvested. The cause and remedies are 
not known. The disease may be of bacterial origin. 

Damping off (Pythium DeBaryanum and other fungi). — 
Young cotton plants may suffer the characteristic soft rot 
of damping off. 



FIBER PLANTS 405 

Sore shin, rhizoctoniose (Rhizoctonia sp.). — Primarily 
this is an ulcerous wound upon the stem near the 
ground, accompanied by reddening or browning of the 
leaves. If the ulcer enters deep into the stem, so as to 
interfere with the ascending sap, it may cause death, 
though this is usually prevented by heiling of the wound 
before the disease has progressed too far. The disease is 
often caused by the attack of rhizoctonia, especially in 
tissues predisposed to such attack by weakness. 

Harrc wing, to aid in drying the surface soil, to some ex- 
tent prevents the attack and development of this fungus. 

A similar disease may also result from purely mechanical 
injuries caused by tools. 

Mosaic, yellow leaf blight, black rust (Physiological). — 
The first signs of this disease are yellowish spots which 
give the leaf a checkered appearance. The discoloration 
occurs first in small areas, which are roughly rectangular 
owing to limitation by the veins, and which are situated 
at points most remote from the main feeding veins. In 
later stages these weakened areas may be overgrown by 
various saprophytic fungi. Usually the centers of these 
spots soon turn brown, and the brown pprt enlarges and 
shows a series of concentric markings. If very dark-colored 
fungi grow upon these spots, they soon become black-coated 
and take the popular name " black rust." 

Kainit, used as fertilizer, often reduces the damage from 
mosaic. 

Red leaf blight (Physiological). — This reddening, re- 
sembling autumnal coloration, occurs most frequently 
toward the season's end and is most common upon poor 
soil. It is due chiefly to lack of nourishment. 



406 DISEASES OF ECONOMIC PLANTS 

Attacks of the mite cause a similar appearance. 

Shedding (Physiological). — This occurs chiefly following 
extremes of either dry or wet weather or following a change 
from one extreme to the other. 

FLAX 

Wilt, fusariose (Fusarium lini Bolley). — A condition 
of soil known as "flax sick" has prevailed in many sec- 
tions of the country to such an extent as to cause the 
abandonment of flax as a crop. This is notably true of 
Iowa, Minnesota, North and South Dakota. On such 
soils flax plants are attacked at any age, and die early or 
late according to the time and intensity of the attack. 1 
Many of the plants in an aggravated attack are killed 
before they appear above the surface of the ground. Such 
field spots become centers of disease ; they enlarge through- 
out the summer, and new plants sicken, wilt, and die around 
their margins, finally giving the entire field a spotted ap- 
pearance. Young plants wilt suddenly and dry up, or 
decay if the weather is moist. Older woody plants become 
sicldy and weak, turn yellow, wilt at the top, and die 
slowly. Such plants are easily pulled up, owing to their 
decayed root system. 

Most of the roots of diseased plants are dead and have 
a characteristic ashen-gray color. If the plant is attacked 
late in the season, this gray color may be limited to one side 
only of the taproot. In such cases the leaves and branches 
on the affected side are blighted. If the disease is sowed 
with the seed upon healthy soil, only a few plants may be 
attacked during the first year, and such plants may be very 

1 Bolley, H. L., N.Dak. Agr. Exp. Sta. Bui. 50, December, 1901. 



FIBER PLANTS 407 

unevenly scattered throughout the field and escape notice 
until late in the season. 

If the weather favor the disease, each new area of infec- 
tion may increase sufficiently to reach plants in several 
adjacent drill rows. These infection areas are nearly 
always circular, and enlarge each year that flax is grown 
thereon. A diseased spot 1-2 m. in diameter the first 
year may become 2-3 m. the second year. Thus only 
a few years are required for the disease to gain complete 
possession of a field. The disease not only persists in a 
field not sown to flax, but the disease areas may even en- 
large when no flax is present. When soil is once infected, 
no way is known to render it suitable for flax again. 

This is essentially a soil disease, and it is spread in the 
ways suggested under soil diseases, notably by soil particles, 
drainage water, and especially diseased flax straw which 
may get into the manure. The chief agent of dissemina- 
tion, however, is the seed. In threshing, the spores of the 
causal fungus, which are abundant upon the dead straw, 
find lodgment upon the seed, especially if it be moist. 

To prevent carrying the disease to land yet uninfected, 
all seed should be disinfected in the following manner : — 

Use formaldehyde at the rate of 1 pound to 40 
or 45 gallons of water. Spread the seed upon a tight 
floor or upon a canvas and sprinkle or spray upon it 
a small amount of the liquid. Shovel, hoe, or rake the 
grain over rapidly. Repeat this spraying, shoveling, and 
raking until all of the seeds are evenly moistened, yet not 
wet enough to mat or gum together. Continue to stir the 
grain, so that the mass may become dry as soon as possible. 
Avoid any excess of moisture. If flax seeds are dipped 



408 DISEASES OF ECONOMIC PLANTS 

in the solution or are allowed to become wet enough to 
soften the coats so that they stick together, they will be 
considerably injured or even killed. 

The solution recommended is strong enough to kill all 
seeds if they are made thoroughly wet or are allowed to stay 
quite damp for some hours. Less than one half gallon of 
solution is required to treat one bushel of seed. It is well 
also to burn all the infected straw and to avoid planting 
too deep. 

By continued selection of seed from resistant plants 
Bolley 1 has developed a variety which is resistant to 
the wilt. 

Alternariose (Alternaria sp.). — This is said by Bolley 
to cause destruction of young plants in damp soil. 

Colletotrichose (Colletotrichum sp.). — This has been 
mentioned by Bolley as very destructive to young plants. 

Rust (Melampsora lini (DC.) Tul.). — This rust shows 
sori characteristic of the rusts. Upon the leaves in early 
season they are yellow or orange. Later black sori appear, 
chiefly upon the stems. Badly affected plants turn 
brown and die earlier than plants not rusted. Large 
injury is not usual, though in 1904 and 1905 considerable 
damage was reported from North Dakota. 

1 Bolley, H. L., N.Dak. Agr. Exp. Sta. Bui. 50, December, 1901. 



TREES AND TIMBER 1 

General Diseases 
DECAY IN LIVE TREES 

Wood decay is always caused by fungi (perhaps rarely 
aided by bacteria) whose mycelium penetrates through 
or between the wood cells, producing enzymes which 
soften the cells or disintegrate the middle layer between 
cells, thus destroying stability of the aggregate as by the 
crumbling of the plaster or the brick of a wall. Within 
the tree this disintegration may occur either to the heart- 
wood or to the sapwood, or to both. 

The life of a tree may be much reduced by decay of the 
heartwood, the main mechanical support. Decay of 
the sapwood further hastens death by interfering with 
the rise of the sap. 

Upon the living tree the natural protection against fun- 
gous invasion is the bark, consisting of cells with specially re- 
sistant walls ; cutinizedor supplied with resin, gum, or other 
repellents. Moreover, the dead bark is not generally nutri- 
tious and does not offer attractive invitation to the fungus. 
The protection thus constituted is normally ample ; but in 
case of removal of the natural protection and exposure of 
either sapwood or heartwood, especially the latter, the path 
is open, and it is through wounds offering such exposure 

1 The facts concerning tree and timber rots are drawn largely from 
the writings of von Schrenk and his associates. 

409 



410 



DISEASES OF ECONOMIC PLANTS 



that rot usually begins in standing timber. Such rots 
might therefore be appropriately termed " wound decays." 





• 

■•*-,*■-■ 
■ • . * -' < . 






Kj^^^W" " jj| 1 **" -^8kj| 


L'.-?t';iyilHl '"^ 



Fig. 174. — Fomes igniarius upon live beech tree. After Atkinson. 



The fungi which cause these decays are, in the main, 
the larger fungi whose fructification is of the toadstool 



TREES AND TIMBER 



411 



type (Fig. 184). After the decay within is well under 
way the spore-bearing toadstools appear upon the surface 
of the diseased parts, and are quite generally recognized by 
lumbermen as a sign of rottenness within. 




FlG. 175. — Stump of limb improperly removed. After Ind. Agr. Exp. Sta. 



A branch, broken or sawed off, split by wind, bruised 
by a falling tree, gnawed by animals, pecked by birds, 
eaten by insects, or wounded in some other way, may re- 
sult in the exposure of heart or sap wood to the fungous 



412 



DISEASES OF ECONOMIC PLANTS 



spore. From this point of invasion the rot spreads in 
every direction. When the rot reaches the trunk, it spreads 
upward and downward and into all branches to which it has 

access. Thus trees, 
hollow with rot, may 
trace their downfall 
to infection of some 
small branch months 
or even years earlier. 
Care should be 
exercised in felling 
trees to avoid injur- 
ing other trees, and 
in case of pruning- 
wounds to apply 
some antiseptic to 
the exposed wound 
to prevent the effec- 
tive germination of 
spores upon its sur- 
face. Suitable anti- 
septics are tar or 
paint. 

Old, diseased trees 
should be cut to prevent spread of infection to other trees. 
Excision of the infected tissue can be practiced in case of 
especially valuable trees. 

The fungi which cause these decays are manifold. In 
some cases one species of fungus grows upon many different 
kinds of wood. Other fungi are more particular as to their 
food supply and are found upon fewer hosts. They chiefly 




Fig. 176. — Wound of properly removed limb be- 
ginning to heal over. Ind. Agr. Exp. Sta. 



TREES AND TIMBER 



413 



belong to two kinds: one bearing its spores upon gills, 
Fig. 184; the other with its spores borne in pores, Fig. 211. 




Fig. 177. 



■Wound of properly removed limb nicely healed over. 
Ind. Agr. Exp. Sta. 



After 



Still others bear their spores upon spines. In describing 
the fructification of the causal fungi for recognition pur- 
poses it is necessary to note especially the stalk, or stipe, and 
the cap or pileus, Fig. 184. A cap with no stalk is " sessile." 



414 DISEASES OF ECONOMIC PLANTS 

Prominent among the rots are these following: — 

Heart rot (Trametes pint (Brot.) Fr.). — In the North 
this rot affects all conifers, invading first the heartwood, 
very rarely the sapwood. The wood is not wholly destroyed 
by the fungus ; but series of small holes with silvery lin- 
ing are noted in early stages. In spruce the color of the 
wood itself is changed to a light purplish gray, later to a 
reddish brown netted with small black lines. Small patches 
of white follow, which later develop into holes, arranged in 
series to correspond with the annual rings, and as the 
disease progresses result in a series of vacant spaces 
separated only by plates. In tamarack the decay finally 
destroys the plates, reducing the whole wood mass to 
mere fiber. 

The sporophores may consist of either brackets or of 
extended sheets with shallow, pit-like pores on the under- 
side. They are cinnamon-brown on the lower surface and 
much fissured and broken on the black, charcoal-like upper 
surface. 

White heart rot (Fomes igniarius (L.) Fr.). — This is 
the most important and widespread of the heart rots, 
and the one which has the widest range of host plants. 
It is known in Alaska, Canada, the United States, and in 
South America to Patagonia, growing upon beech, aspen, 
willow, mountain maple, hornbeam, white elm, sugar maple, 
red maple, silver maple, striped maple, yellow birch, butter- 
nut, black walnut, oaks, apple, and hickory. The amount 
of damage done by it is beyond estimation. In many 
cases almost the entire timber stand is ruined. Actual 
count has shown 90 to 95 per cent of otherwise market- 
able trees valueless. 




Fig. 178. — Fomes igniarius upon maple. After von Schrenk. 



416 DISEASES OF ECONOMIC PLANTS 

The rot, while chiefly of the heartwood, may, when 
started, encroach upon the sapwood, even to the youngest 
layers, and death may result by weakening the tree to the 
breaking point. 

The causal fungus enters through wounds, particularly 
broken stubs, and usually produces its sporophore at these 
points after the rot has extended a meter or so in both 
directions from the infection point. The first sure external 
sign of the disease is the presence of the sporophores, al- 
though sounding with the ax may sometimes be relied upon. 

The sporophores, numbering sometimes as many as 
twelve on a tree, are shelving, hoof-shaped bodies from 
25 to 30 cm. wide. The upper surface is brown, in later 
stages black, hard, smooth, concentrically marked with 
age, finally seamed and cracked. The pores are in layers, 
approximately annual, and may be 50 or even 80 in number. 
The lower surface is gray to red-brown. 

The trunk in cross section shows rot at the center; the 
wood becomes soft and pulpy. The decayed region is ir- 
regular in outline and bounded by narrow black layers. The 
tree is rarely hollow, but remains filled with the decayed 
wood. Young trees which have no dead branches to admit 
the fungus are usually immune. 

Infective material should be burned, wounds avoided, 
and excision practiced in case of valuable trees. 

Red heart rot (Polyporus sulphureus (Bull.) Fr.). — 
The conifers, also oak, cherry, chestnut, maple, walnut, 
butternut, alder, locust, apple, pear, and many other trees 
are affected. It is very widely distributed and destructive. 

The many-pored edible sporophores consist of a series 
of overlapping shelves, two to twenty, or possibly more, 



TREES AND TTMBER 



417 



with the upper surface in early stages a bright orange-red ; 
later they are sulphur-yellow both above and below. The 




Fig. 179. — Polyporu3 sulphureus showing effect upon wood of oak tree. After von 

Schrenk. 



upper surface when bruised is brown. The sporophore is 
soft and fleshy when young, growing harder with age until 

2 E 



418 DISEASES OF ECONOMIC PLANTS 

at maturity it is brittle. This fungus abounds on knots 
and stumps. 

The rotted wood resembles a red-brown charcoal and 
bears concentric and radial cracks due to shrinkage follow- 
ing the decay. In these cracks are large sheets of fungous 
wefts. 

Diseased trees should be cut and burned to prevent 
infection. 

Piped rot (Fungus sp.). — The oak, chestnut, beech, and 
birch are susceptible to this rot. The sporiferous stage of 
the causal fungus has not been recognized. The rot, 
limited to the heartwood, is characterized by irregular, 
small, pocketlike patches of white fiber. 1 These regions 
first appear in the wood as small, lenticular areas which 
increase, coalesce, and change into small pockets. These 
frequently become filled with a dark, red-brown myce- 
lium. The speckled 'character of the wood is a distinctive 
mark. 

Heart rot (Fomes nigricans Fr.). — The birch, willow, 
and aspen, from Maine to Oregon, are affected. 

The rotted heartwood is reddish brown and very soft 
and spongy. The disease eventually progresses into the 
sapwood, reaches the bark, and kills the tree. 

The pore-bearing sporophores are few, hoof-shaped, large, 
25-30 cm. wide, and woody, much like those of Fomes 
igniarius. 

White rot (Hydnum erinaceus Bull.). — Although upon 
many species, oaks are chiefly affected. The rotten wood 
is soft and wet and with numerous holes full of light yel- 
low floccose mycelium. The fleshy sporophores are white, 

1 Von Schrenk, H„ U.S. Dept. Agr. Bur. Plant Indus. Bui. 149. 



TREES AND TIMBER 419 

1 to 25-30 cm. in diameter, nearly spherical, and consist 
chiefly of immense numbers of white spines upon whose 
surfaces the spores are borne. 

Heart rot (Fomes fulvus Fr.) . — In Missouri and Arkansas 
this heart rot is found upon the river birch and a num- 
ber of other trees. The wood is brown, and crumbles on 
crushing. It extends from 3-4 m. above and below the 
sporophores. These are pore-bearing, triangular in section. 
The upper surface is very hard and bears fine, irregular 
fissures parallel to the edge. When mature, the upper 
surface is red-brown. The pores are barely visible without 
a hand lens. 

Rot (Polyporus subacidus Peck). — This is a rot of dead 
logs as well as living trees, which often enters through the 
roots. 

The decayed wood is moist, spongy, and bears cavities 
of various size and shape lined with a tough mycelial felt, 
which is yellow inside. In early stages the wood is black- 
spotted. The black spots later give way to larger white 
spots surrounded by a straw-colored frayed region. The 
sporophores are sheet-like and bear shallow, straw-yellow 
pores. 

Soft rot (Polyporus obtusus Berk.). — The black oaks (Q. 
Marylandica and Q. velutina) are chiefly affected by this 
rot, which is found in Missouri, Arkansas, Iowa, Tennes- 
see, Mississippi, New Jersey, and Maryland. 

The causal fungus enters through the burrows of a wood 
borer. The heartwood turns light yellow, then white, 
and becomes brittle. Strings and sheets of white mycelium 
are found in the wood. Death results either from diminu- 
tion of water supply or from breaking of the trunk. 



420 



DISEASES OF ECONOMIC PLANTS 



Heart rot (Fames Everhartii Ell. & Galloway). — This 
rot closely resembles that caused by Fomes igniarius. 




Fig. 180. — Tree weakened by Fomes fomentarius. After Atkinson. 



Large, rusty-brown, woody sporophores, red-brown below, 
grow from wounds and bear very small pores. 



TREES AND TIMBER 



421 



White rot (Polyporus sguamosus (Huds.) Fr.). — In 
Europe this rot affects several species of maples, the pear, 
oak, elm, walnut, linden, willow, ash, birch, beech, and 
horse-chestnut. In 
America it has been 
reported from Min- 
nesota. The wood 
becomes unusually 
white and bears scat- 
tered series of white 
lines. 

The nearly circular 
fruiting bodies are 
stalked and often at- 
tain a diameter of 15 
cm. When young, 
they are soft, but 
later become very 
tough. The upper 
surface is scaly and 
rough. 

Sapwood rot 
(Fomes fomentarius 
(L.) Fr.). — This rot 
abounds throughout the northern part of the United States, 
as one of the most common diseases of deciduous trees, 
chiefly affecting the beech, white, paper, and yellow birches. 

Decay begins in the outer sapwood and proceeds inward. 
The wood is marked by irregular black lines, the boundaries 
between diseased and normal wood. When wholly rotten, 
the wood is soft and spongy and light yellow in color. 




Fig. 181. — Fomes fomentarius showing hoof-shaped 
sporophore. After Atkinson. 



422 



DISEASES OF ECONOMIC PLANTS 



The pore-bearing sporophores are hoof-shaped, smooth 
above, and concentrically ridged and gray. Below they 

are red-brown. 

Rot (Fomes ap- 
planatus (Pers.) 
Wallr.). — The 
shelving, pore- 
bearing sporo- 
phores are very 
large, woody, and 
grayish to brown 
above, and are 
commonly found 
on dead wood, 
more rarely upon 
live trees. 

Rot (Poly- 
porns pinicola 
(Schwartz) Fr.). 
— The causal 
fungus is of 
world-wide dis- 
tribution upon 
conifers, espe- 
cially spruce, 
pine, fir, and hemlock. It occurs also upon birches and 
other deciduous trees. Entrance is made through wounds 
of any kind. The rotted wood is brittle, cracked, and 
permeated by numerous sheets of mycelium. In early 
stages of decay it passes through red-brown to dark-brown, 
then small, white areas of numerous shapes and irregu- 




Fig. 182. 



Fomes applanatus upon trunk of dead tree. 
After Freeman. 




V 



Fig. 183. — Fruiting body of Polyporus pinicola upon log rotted by the fungus.' 
After von Schrenk. 



424 DISEASES OF ECONOMIC PLANTS 

larly scattered appear. The sporophores vary from 2.5-30 
cm., averaging 10-15 cm., are bracket-shaped and lobed. 
The young lobes are bright red to pale yellow, old ones 
dark red-brown. The lower surface is pale and smooth; 
watery when bruised. 

Canker (Nummularia and Nectria cinnabarina (Tode) 
Fr.) . — The cankers caused by these fungi occur either upon 
branches or roots and may be found upon nearly all species 
of deciduous trees of which they are wound parasites. The 
spores are borne on soft, bright red knobs, or in another 
form in pear-shaped perithecia. Infective material should 
be burned. 

ROOT ROTS 

Fungi similar to these already considered may also at- 
tack the roots of trees and thus cause death without any 
previous rotting of the trunk wood. Prominent among 
such diseases are the following : — 

Armillariose (Armillaria mellea Vahl). — The fungus 
usually enters the root through wounds, and grows in 
the cambium, through which it spreads until it encircles 
the tree. As its growth proceeds the layers adjacent to the 
cambium become dry, and the top of the tree is killed by 
stoppage of its water supply. A characteristic accompani- 
ment is the profuse development of string-like, hard, black 
mycelial strands which permeate the soil near the base of 
the affected tree. From the mycelium around the base 
of the tree rise the numerous white-gilled, honey-colored 
sporophores, their viscid tops necked with white ; the stems 
swollen and with a ring (annulus). 

This disease may spread for long distances through the 



TREES AND TIMBER 



425 



soil by means of the fine roots and infect neighboring trees. 
Upon newly cleared land diseased roots of forest trees may 
be a source of infection to fruit trees subsequently grown 
thereon. 
Polyporose (Polyporus versicolor). See p. 429. 




Fig. 184. — Armillaria mellea attacking a tree. After Freeman. 

Red rot (Fomes annosus Ft.). — Though not very de- 
structive in this country, this fungus has been found on 
many of the pines, where it brings about a red rot of the 
root system, which ultimately results in the death of an 
affected tree. The fruiting bodies form small, cup-shaped 
or irregular masses on the roots or around the base of the 



426 



DISEASES OF ECONOMIC PLANTS 



trunk. The fungus has also been found growing on 
trees many years after they had died. Neighboring trees 




Fig. 185. — Log rotted by Polyporus Schweinitzii. After von Schrenk. 

generally become infected from a diseased tree, through the 
small fibrous roots. 

Root rot (Polyporus Schweinitzii Fr.). — A destructive 
root rot of spruce, fir, arbor vitae, and pine, by weakening the 
root or trunk, leads to the overthrow of the tree by wind. 



TREES AND TIMBER 427 

The point of attack is always the root, through the heart 
of which invasion is made into the trunk. This often leads 
to one-sided decay of the trunk's heartwood. The wood is 
rendered very brittle, yellow, and later of cheesy character, 
so that it can readily be cut cross grain when wet or re- 
duced to a powder when dry. 

The pore-bearing sporophores, which appear in July or 
August, are from 10-35 cm. across, growing either from the 
roots or the trunk. If from the trunk, they are sessile ; 
from the roots, stalked. The fresh spore layer is rose-col- 
ored, and turns dark red if bruised. 

This disease is very common throughout northern for- 
ests. In Europe, where it is greatly dreaded, it is cus- 
tomary to prevent its spread by trenching. Groups of 
infected trees and trees near them may be cut to advan- 
tage to protect other trees. 

Root rot, ozoniose (Ozonium omnivorum Shear). — 
Elm, basswood, oak, cottonwood, mesquite, china tree, 
mulberry, apple, and pear are affected by this rot, which 
has been described and discussed on page 401 . 

Root rot, dematophorose (Dematophora necatrix Hartig). 
— A disease described on page 172 affects a large number 
of species of trees, among them mulberry, fig, apple, pear, 
and cherry, as well as many wild species. 

Thelephorose (Thelephora galactina Fr.) . — Noted in 
the Ozarks primarily upon the oak, but attacking fruit 
trees as well, this rot much resembles dematophorose. 

DECAY OF DEAD TREES OR DEAD PARTS 

While decay of dead trees cannot be regarded strictly 
as a condition of disease, but rather as a post-mortem 



428 



DISEASES OF ECONOMIC PLANTS 



change, a word is clue to it on account of its vast impor- 
tance, involving, as it does, all structural wood. The fact 
that the railroads use more than 110,000,000 ties annually, 
and that the number of posts in use is approximately 






kj; 



Fig. 186. — Dry rot fungus (Merulius lacrymans) ; on the right the mycelium is 
visible as white strings. After Freeman. 



4,000,000,000, necessitating an annual replacement of 
some 500,000,000 in the United States, indicates the enor- 
mous money values involved. 

This kind of decay is brought about by agencies similar, 
sometimes identical, with those causing rot in living trees, 



TREES AND TIMBER 429 

It can be prevented by impregnating the wood with vari- 
ous antiseptics, as creosote or zinc chloride. 1 

A few of the chief causes of the decay of dead wood are as 
follows : — 

Polyporose (Polyporus pinicola). Seep. 422. 

Dry rot, meruliose (Merulius lacrymans (Jcq.) Fr.). — 
One of the most common and destructive of all the rots 
of structural timber, this renders the wood spongy and 
brownish. If very moist, a profuse superficial pure white 
mycelium may develop, at first loosely, later in dense sheets 
or strands. The sporophores are flat, at first white, later red, 
and still later yellow-brown. The spore-bearing surface 
carries shallow pores penned between folds and wrinkles. 

Sap rot (Polystictis versicolor (L.) Fr.) . — In addition to 
its parasitic life upon the chestnut and catalpa, this fungus 
grows as a saprophyte upon all kinds of deciduous woods, 
and is " regarded as the most serious of all wood-rotting 
fungi which attack the dead wood of broad-leaf trees. 2 
It destroys probably 75 per cent or more of the broad- 
leaf species of timber used for tie purposes." " When- 
ever broad-leaf species of wood are used for fencing for 
posts or poles, or for any purpose where they come in con- 
tact with the soil, they are sure to be attacked sooner or 
later by Polystictis versicolor." 

Polyporose (Polyporus pergamenus Fr .) . — This fungus is 
similar to Polystictis versicolor, and of great importance, 
appearing upon cut timber or on large wounded surfaces 

*For details see Sherfesee, W. F., Bui. 78, Forestry Service, November 
11, 1909. 

2 Von Schrenk, H., and Spaulding, Perley, U.S. Dept. Agr. Bur. Plant 
Indus. Bui. 149. 



430 



DISEASES OF ECONOMIC PLANTS 



of standing trees, especially following fires. It is found 
throughout the United States on all deciduous woods. 




Fig. 187. — Trees infested with mistletoe. Courtesy of the School of Botany of the 
University of Texas. 



Very numerous genera and species of fungi other than 
those mentioned above can also bring about similar changes. 



TREES AND TIMBER 431 

Mistletoe (Phoradendron flavescens Nutt). — While not 
generally considered a pest, this parasite under favorable 
weather conditions may become so, especially upon 
trees in lawns and parks. It usually attacks the smaller 
branches of the trees, and thus cuts off the nourishment 
from their tips and eventually causes this portion to 
die. The general effect is to spoil the beauty of the tree. 
About thirty different kinds of trees are attacked, and the 
parasite can be carried easily from one host to another. 

To destroy mistletoe the infected branches should all be 
cut from the trees and no berries allowed to mature, thus 
preventing dissemination of the pest by birds. 



Special Hosts 
ASH 

White rot (Polyporus fraxinophilus Peck). — In Missouri, 
Nebraska, and Kansas in some localities this disease 
affects 90 per cent of the trees. It prevails in the 
Mississippi valley and east to the Atlantic. The heart- 
wood first darkens, and later becomes soft, pulpy, and yel- 
lowish. The shelving, pored sporophores, 5-10 cm. long 
and nearly triangular in section, are numerous, chiefly 
near stubs or wounds, appearing soon after infection. The 
old upper surface is brown or black, and very hard. Trees 
of any age are susceptible, but those over 10 cm. in diameter 
are most subject to attack. Diseased trees should be cut 
down, or excision practiced, and the hole filled with tar. 

Rust (Puccinia fraxini (Link) Arthur) . — This is a rust 
which may be recognized by the orange-colored cluster 
cups upon the much-swollen parts of the leaves and petioles 



432 DISEASES OF ECONOMIC PLANTS 

of nearly all species of ash. The winter condition is found 
upon marsh grass, Spartina. 

The injury is not usually large, but in seasons favorable 
to the disease defoliation may result. Diseased leaves 
should be collected and burned. 

Phyllostictose (Phyllosticta viridis Ell. & Kell.). — Brown 
spots, 5-10 mm. in diameter, with conspicuous yellow 
borders and minute black pycnidia, appear upon the leaf- 
lets. Defoliation may result. 

Leaf spots. — Leaf spots due to several species of fungi 
are frequently seen, but not in destructive form. Among 
the causal fungi are : Glceosporium, Shseropsis, Septoria. 

BIRCH 

Sapwood rot (Polyporus betulinus Fr.). — Several species 
of birch are affected by this rot, which is of wide distribu- 
tion in the northern United States. The fungus enters the 
sapwood from the bark through wounds or through the 
lenticels, and progresses inward. The yellowish, cracked, 
diseased wood crumbles when fully decayed. 

Rust (Melampsora betulina (Pers.) Tul.). — This is much 
like the willow rust. See p. 450. 

BUTTERNUT 

Gloeosporiose (Glceosporium juglandis (Lib.) Mont.). — 
The affected leaflets bear circular dead spots, indefinitely 
bordered, and defoliation results. The disease spreads very 
rapidly throughout the tree, and to other trees. 

CATALPA 

Leaf spot (Phyllosticta Catalpce Ell. & Mart.). — Affected 
leaves bear round brown spots, often with a yellow- 



TREES AND TIMBER 



433 



gray border. The spots, from 3-6 mm. in diameter, 
often coalesce to form large blotches which are fragile, 
sometimes dropping from the leaf. Young leaves develop 
poorly and are deformed, while severe infection may cause 
complete defoliation of the tree. 




Fig. 188. — " Cedar apple," gall of the rust fungus. Original. 

Macrosporiose (Macrosporium Catalpce Ell. & Mart.). — 
This spot is scarcely distinguishable from phyllostictose 
except through the absence of pycnidia and the presence of 
a scant quantity of black mold. 

Powdery mildew, microsphaerose (Microsphcera elevata 
Burr). — This shows the usual powdery spots with black 
perithecia. 

Rhizoctoniose. Seep. 61. 
2f 



434 



DISEASES OF ECONOMIC PLANTS 



Soft heart rot (Polystictis versicolor (L.) Fr.). — The 
wood at the center of the tree is discolored and dis- 
integrated, becoming eventually straw-colored and soft. 




Fig. 189. — Cross cut of cedar log showing effect of Polyporus juniperinus. 
After von Schrenk. 



The sporophores appear near the wound which afforded 
entrance. They are sessile, grouped, soft hairy above with 
alternate bands of light and dark color. When old, they 
are tough with edges curled in. See also p. 429. 



TREES AND TIMBER 



435 



CEDAR, RED 

Rust (Gymnosporangium, various species). — The "cedar 
apples," familiar upon the red cedar, are usually of but 
small significance to the cedar tree itself unless exception- 
ally abundant. See apple rust. 




Fig. 190. — Longitudinal section of cedar showing effect of Polyporus juniperinus. 
After von Schrenk. 



White rot (Polyporus juniperinus v. Schrenk). — In 
this disease long holes appear in the heartwood, extend- 
ing longitudinally with a partition of sound wood be- 
tween. These cavities may eventually unite to form tubes 
throughout the tree. The wood between one cavity and 



436 DISEASES OF ECONOMIC PLANTS 

the next is not the normal red, but is somewhat t 
and the holes themselves are coated with a brillia ;-. \\ 
lining. The holes, partially filled with a velvety %eddisu- 
yellow mycelium, may be from 4-9 cm. long. Tile pore 
bearing sporophore is hard and woody, rough above, lai 
fissured, yellow-brown at the margin, later deep brow. 
The pore layer is yellow to brown. 

Red rot, pecky cedar (Polyporus carneas Nees) .- -Though 
more common than white rot, this has been fo..nd in 
Missouri, Arkansas, Kentucky, Tennessee, Virginia, New 
York, and Mississippi. 

The wood is full of pockets of brown, brittle wood, vary- 
ing from a centimeter to a meter or so in length. The 
sporophore, formed in the cavities under dead branches, is 
from 0.5-35 cm. in length by 1 cm. wide. The pore-bearing 
layer is flesh colored. 

These two diseases of the cedar taken together have been 
estimated to cause 60 per cent loss in some; localities. 
Since they are caused by wound parasites, the removal of 
diseased trees and the destruction of sporbphores is 
recommended. 

CHESTNUT 

Bark disease 1 (Diaporthe parasitica Murrill). — First 
noted in 1904 by Murrill in New York, this disease is 
now known in New York, New Jersey, Delaware, Col 
necticut, Rhode Island, Maryland, and Virginia, and' 1 
rapidly spreading in every direction. In Brooklyn 16,69o 
trees were killed on 350 acres, and the loss in and about 

*• Metcalf, H., and Collins, J. F., U.S. Dept. Agr. Bur. Plant Indus. Bui. 
141. 



TREES AND TIMBER 



487 



■rk City is placed at five to ten million dollars. The 

iqu pin and chestnut alone are susceptible. The attack 

>d mad upon the bark through wounds, but twigs and 

leaves are not directly affected. From the point of attack 

" spreads in all directions until the diseased parts meet on 




Fig. 191. — Map showing the distribution of the chestnut bark disease: black shows 
area of severe infection ; round dots, presence of disease prior to 1909 ; + indicates 
■* the spread of the disease during 1909. After Metcalf . 



.jhe opposite side of branch, thus girdling the twig. Dead, 
Jiscolored, sunken patches with numerous yellow, orange, 
or reddish-brown pustules are produced; spores are extruded 
in greenish or yellow horns. The appearance of the fun- 
gus upon the trunk indicates speedy death, but if small 
branches are first diseased, the tree may live for a few years. 



438 DISEASES OF ECONOMIC PLANTS 

Infection is supposed to be spread through nursery stock, 
and when once established, no means of stopping it is known. 
Only preventive measures can be taken, such as destruction 
of diseased trees by fire, careful inspection of all nursery 
stock, and excision in the case of isolated trees which are 
considered valuable enough to justify this mode of treat- 
ment. 

Septoriose (Septoria ochroleuca B. & C). — Small dead 
spots 3 mm. in diameter are produced upon the leaves, 
and premature defoliation results, injuring the beauty of 
the tree. 

Anthracnose, leaf spot (Marsonia ochroleuca B. & C). — 
The characters of this disease are small bleached areas with 
spore pustules in them. It has been quite injurious to 
nursery varieties. 

Bordeaux mixture is advised. 

Monochetiose (Monochetia pacyspora Bubak). — This leaf 
spot is very abundant in forests, and causes much loss 
of vigor to the tree. It is recognized as large, 1-5 cm. 
circular spots with irregular concentric marking. No 
treatment is possible in forests, but isolated trees can be 
protected by spraying. 

COTTONWOOD 

Rust (Melampsora). — In general this resembles the 
willow rust. See p. 450. 

ELM 

Leaf spot, dothidellose (Dothidella ulmea (Schw.) Ell. & 
Ev.). — The leaf spots are 1-3 mm. in diameter, and in 
each spot is a cluster of small, black, rounded, slightly ele- 



TREES AND TIMBER 



439 



vated perithecia, the cluster surrounded by a border of 
dead tissue. Premature defoliation results. The disease 
is very abundant in all parts of the United States. In- 
fected materials should be burned 
in the fall. 

Powdery mildew, uncinulose. See 
oak. 

Powdery mildew, phyllactinose. 
See oak. 

FILBERT. See hazel. 

FIR 

Rust (Aecidium elatinum Alb. & 
Schw.). — This cluster-cup fungus 
has been noted in Minnesota. 1 It 
produces bushy distortions, "witches' 
brooms," by causing profuse branch- 
ing of the affected part of the tree. 
These abnormal branches soon lose 
their leaves, and cluster cups are 
produced upon them. The brooms 
are perennial and increase in size 
each year, in some cases largely 

covering a whole tree with the brooms. In such cases the 
trees are stunted and may even be killed. Infection may 
be reduced by destruction of the spore-bearing branches. 

Canker (Dasyscypha resinaria (Ckle. & Phill.) Rehm). — 
Swollen cankers occur in the stems and branches, even 
girdling the main trunk and killing the tree. After the 

1 Freeman, E. M., Minn. Plant Dis., p. 277. 




Fig. 192. — Elm leaf -spot. 
After Heald. 



440 DISEASES OF ECONOMIC PLANTS 

branch is dead the causal fungus fruits in small disks, 
orange-colored within, about 4-6 mm. wide and high. 

HAZEL 

Black knot (Cryptosporella anomala (Peck) Sacc). — In 
1892 Halsted noted black knot as destructive to several 
hundred trees in New Jersey, and in 1893 Humphry 1 
described the same disease as upon hazel canes in Massa- 
chusetts. It is characterized by numerous small elliptical, 
warty emergences upon the bark of the diseased branches. 
The diseased portions are sunken, owing to the contraction 
of the inner bark to a mere line. The girdling produced 
results in death of the affected canes and general injury 
similar to that produced by plum knot. Affected branches 
should be cut and burned. 

HORSE-CHESTNUT 

Leaf spot, phyllostictose (Phyllosticta sphoeropsidea Ell. & 
Ev.). — Unsightly spots upon the leaflets and premature 
defoliation render this the most conspicuous disease of this 
tree. The brown spots are at first circular, but as they 
enlarge are limited by the larger ribs, thus becoming nearly 
rectangular. Pycnidia may be seen with a lens. This is 
a decided nursery pest. 

Five applications of Bordeaux mixture have much reduced 
the spotting. 

LINDEN 

Leaf spot, cercosporose (Cercospora microsora Sacc). — 
Small circular or large irregular dead spots of the leaf 

1 Humphry, J. E., Mass. (Amherst) Agr. Exp. Sta. Rpt. 10, January, 
1893. 



TREES AND TIMBER 441 

indicate the presence of this disease. It has been reported 
as destructive in Massachusetts, New Jersey, and New 
York. Two sprayings in Massachusetts resulted in longer 
retention of the foliage and lessened infection. It was 
estimated that two sprayings will give a gain of from 2 to 5 
per cent in growth and development. 

LOCUST 

Heart rot (Fomes rimosus Berk.). — From Massachusetts 
to New Mexico, over the entire black locust territory, 
this heart rot prevails. It is a yellow rot extending from 
the center outward in radial lines through the medullary 
rays; the hard flinty wood is reduced to a soft yellow cheesy 
mass, spongy when wet. The pore-bearing, shelving, hoof- 
shaped sporophores develop chiefly from the burrows of 
the locust borers or from stubs. The young portions are 
light brown; older parts, dark to black and fissured. The 
lower side is dull red-brown. 

The rot ceases with the death of the tree, and posts made 
from diseased wood do not continue to rot. 

LOCUST, HONEY 

Leaf spot (Leptostroma hypophylla B. & Rav.). — The 
leaflets become covered with small black specks; some 
turn yellow and fall. 

MAGNOLIA 

Colletotrichose (Colletotrichum sp.). — Circular dead spots 
are produced upon the leaves and upon the young branches, 
killing the foliage and twigs. 



442 



DISEASES OF ECONOMIC PLANTS 



MAPLE 

Leaf spot, phyllostictose (Phyllosticta acericola C. & E.). — 
A large proportion of the leaf may become involved, 
causing premature defoliation which materially lessens the 




Maple tar spot. After Heald. 



value of the tree for ornament or shade. The silver maples 
are especially susceptible, and their sale has thereby been 
reduced. The leaf spot was first noted in 1874 and is dis- 
tributed throughout the United States. The blackish, 
sub circular spots as they enlarge change to brown and later 



TREES AND TIMBER 443 

to dirty white in the center with black borders. Small 
black pycnidia may be seen in the central regions of the 
mature spots, which are from 10-14 mm. in diameter. 

Burning diseased leaves is recommended, accompanied by 
use of Bordeaux mixture when economy allows. 

Tar spot, rhytismose (Rhytisma acerinum (Pers.) Fr.). — 
Thick, shining, irregular black spots 1-1.5 cm. across 
appear on the leaves in late summer and cause them to 
fall prematurely, thus weakening the tree. Considerable 
damage is often done to nursery stock. 

The leaves should be raked together and burned in the 
fall. 

Leaf spot, rhytismose (Rhytisma punctatum (Pers.) Fr.). — 
In this leaf spot the causal fungus forms several small 
black dots upon the leaves as contrasted with the one large 
black blotch of the tar spot. 

Anthracnose, gloeosporiose (Glceosporium apocryptum Ell. 
& Ev.). — Nursery maples have been seriously injured by 
this anthracnose. The tips of leaves of pruned twigs turn 
yellow, then blacken and die as though frosted. Young leaves 
and shoots are killed and by their death induce abnormal 
branching, resulting in a compact " head." The disease 
seems limited to young trees. 

Bordeaux mixture is advised, three or more sprayings. 

Powdery mildews. See Oak. 

MULBERRY 

Bacteriose (Bacterium mori Boy. & Lamb.). — Upon the 
leaf small reddish brown 1 spots, pellucid when moist, are 
produced. The twigs and even entire trees are stunted and 

1 Conn. Agr. Exp. Sta. Rpt. 1904, p. 319. • 



444 DISEASES OF ECONOMIC PLANTS 

yellowed. Cankers may almost or quite girdle the stem, 
the diseased area becoming dark. Prune as for blight of 
pear. 

OAK 

Leaf curl, taphrinose (Taphrina ccerulescens (Desm. & M.) 
Tul.). — Though close kin to the peach curl, only a small 
proportion of each leaf in spots 1-2 cm. in diameter is in- 
volved. Defoliation may result in extreme cases, and con- 
tinued disease each year may cause death. Affected leaves 
should be burned and the tree sprayed as for peach curl if 
the tree value warrants it. 

Powdery mildews, microsphaerose (Microsphcera) . — These 
appear late and do little harm except upon nursery stock. 

Flowers of sulphur or Bordeaux mixture are useful. 

OSAGE ORANGE 

Rust (Physopella Fid (Cast.) Arthur). — The sori which 
are scattered thicldy over large areas of the lower side of 
the leaf are small, 0.1-0.3 mm. in diameter and are pale 
cinnamon-brown. This is known from South Carolina to 
Texas. 

PECAN 

Scab, fusicladiose (Fusicladium effasum Wint.). — Twigs, 
leaves, and nuts are affected in the Southern States, 1 
particularly Florida, Louisiana, Georgia, Oklahoma, and 
Texas. Upon leaves and petioles dead spots, distortion, 
and defoliation are caused. The new growth of twig is 
often killed, but the greatest injury is to the nuts. 

1 Orton, W. A., Sci. n. s. 21, 503, March 31, 1905. 



TREES AND TIMBER 445 

Spraying has proved effective. 

Microsphaerose (Microsphcera alni Wallr.). — Certain 
years in the South the pecan crop has been practically 
destroyed by this mildew. It is recognized as a flour- 
like, white coating particularly damaging over the young 
nuts. 

Spraying with Bordeaux mixture before the fungus 
appears is effective. Burning of infected fall refuse is also 
helpful. 

PINE 

Bluing (Ceratostomella pilifera (Fr.) Wint.). — The char- 
acteristic symptom, bluing of the sapwood, begins in 
August and September after the trees have been attacked 
by beetles. 1 The blue color starts near the base of the tree 
and gradually spreads upward until the entire sapwood is 
blue. The cause is the presence of the mycelium of the 
above-named fungus, which gains entrance through openings 
made by the beetle and is initiated by spores carried 
by the beetle. 

Blue wood is as strong as normal green wood, is tougher, 
and when dry, it will last as long; but when wet, it rots 
rapidly. 

Hypodermose (Hypoderma Desmazieri Duby). — The 
needles die from the tips toward the bases, becoming first 
reddish, then gray. Black lines which extend lengthwise 
of the leaves are the ascus-bearing organs. 

Premature defoliation results. 

Leaf blight, twig blight (Lophodermium brachysporwn 
Rostr.). — In Maine the leaf blight has been noted as 

1 von Schrenk, H., U.S. Dept. Agr. Bur. Plant Indus. Bui. 36. 



446 DISEASES OF ECONOMIC PLANTS 

destructive to a considerable number of small trees and in- 
juring the lower branches of large trees; serious damage 
from it, however, is not common. 

Fusariose, damping off (Fusarium sp.). — The general 
characters are these mentioned under damping off. It is 
serious in Vermont, New York, Missouri, and probably in 
many other states, killing the seedlings in nurseries as 
soon as they appear above ground. 

The beds should be given all ventilation possible. A top- 
dressing of sterilized sand sprinkled over the beds immedi- 
ately after germination resulted in 30 per cent of disease 
against 42 per cent in the untreated part. Perhaps the best 
results have been attained by the use of copper sulphate 1 
pound and lime 10 pounds, 1 and by sulphuric acid 1 ounce 
to 1 gallon of water, either of these applied to the soil of 
the seed bed before planting and again after the plants 
are up. 

Rust, peridermiose (Peridermium Cerebrum Peck of Cro- 
nartium Quercus). — Swollen areas occur upon the branches 
and young stems which are gradually killed. The gall-like 
growth sheds an abundance of orange-colored spores each 
spring. In some sections it kills many trees, chiefly by 
its interference with the sap current. The swellings are 
perennial and may last for many years. One stage of this 
rust occurs upon the oaks. 

Peridermiose (Peridermium acicolum Und. & Earle, of 
Coleosporium solidaginis (Schw.) Thum.). — Another species 
of Peridermium of no special significance occurs upon leaves, 
producing small, sac-like, tubular outgrowths which contain 

1 Spaulding, Perley, U.S. Dept. Agr. Bur. Plant Indus. Circ. 4, April, 
1908. 



TREES AND TIMBER 



447 



the spores. This is the cluster-cup stage of a rust which 
appears later in the season upon goldenrods and asters. 

Red rot 1 (Polyporus ponderosus 
von Schrenk). — Upon dead trees 
this rot starts just under the bark, 
usually near the tree top, often fol- 
lowing " bluing." The wood is at 
first wet and soggy, but soon becomes 
brittle, so that it crumbles readily. 
The cracks become filled with felted 
fungous threads. The sporophores 
first appear as fleshy knots, soon red, 
which widen to pore-bearing shelves. 

Cladosporiose blight (Cladosporium 
herbarum (Pers.) Link). — The ter- 
minal leaflets die and curl and the tip 
of the stem is killed. Dark patches 
of hyphse appear upon the dead parts. 

POPLAR 

Rust (Melampsora populina (Jcq.) 
Lev.). — This is similar to willow rust. 
See p. 450. 

Powdery mildew, uncinulose. See 
willow. 

Leaf blight, marsoniose (Marsonia 
Populi (Lib.) Sacc). — Primary in- 
fection occurs upon the leaves, re- 
sulting in small, 3-8 mm., circular, black dead spots which 
are quite definitely bordered. As the leaves die, patches 

1 von Schrenk, H., U.S. Dept. Agr. Bur. Plant Indus. Bui. 36, 1903. 




Fig. 194. — Pine needle 

bearing cluster cup of 

rust, enlarged. After 
Clinton. 



448 DISEASES OF ECONOMIC PLANTS 

upon the stems also turn black and die. Infection pro- 
ceeds to the supporting twigs and may result in dead 
patches of bark upon quite large shoots. 

Cutting and burning infected twigs is advised. 

SASSAFRAS 

Heart rot (Fomes Ribis (Schum.) Fr.). — Spaulding 
in 1907 l described this rot as a serious injury to sassafras 
in Missouri. It is also found upon stems and roots of 
various shrubby plants, as rose, currant. By means of a 
wound the attack is made upon exposed heartwood, 
proceeding slowly into the sapwood. The sassafras is 
thus immune until it reaches an age bearing heartwood. 
The decaying wood is abnormally light in color and 
slightly reddish, and the affected region is bounded by 
a narrow black zone. Trees sometimes die from the 
attack. 

The causal fungus has been reported in America from 
Kansas, Missouri, New York, and New Jersey. 

SYCAMORE 

Gnomoniose (Gloeosporium nervisequum (Fckl.) Sacc. of 
Gnomonia veneta (Sacc. & Speg.) Kleb.). — First noted in 
1848, this anthracnose is very widely distributed from New 
Jersey to California and Mississippi. In extreme cases 
it may so weaken the trees as to cause their death. The 
scorched appearance of the leaves and defoliation render 
the trees unsightly. Just before they become full-grown 
the leaves give the first indication of the attack. Begin- 
ning near the veins or ribs or upon the petiole, the disease 

1 Spaulding, Perley, Sci. n. s. 26, 479. 



TBEES AND TIMBER 



449 



causes a stoppage of the water supply to the more distant 
portions of the leaf, resulting 
in dead areas. 

Dead twigs should be pruned 
out, and infected material col- 
lected and burned. Spraying 
with Bordeaux mixture may 
be practiced if the expense is 
warranted. 

Powdery mildew. See oak. 

BLACK WALNUT 

Anthracnose, Gnomoniose 

(Marsonia juglandis (Lib.) 
Sacc. of Gnomonia juglandis). 
— Conspicuous brown spots, 
2-4 mm. in diameter, appear 
upon the leaflets, which soon 
yellow and fall. Upon the 
lower sides of the leaf spots 
are small, concentrically ar- 
ranged, black acervuli. 

The disease has been trouble- 
some in Delaware, Iowa, Mary- 
land, and West Virginia. 

WALNUT, ENGLISH 

Pseudomonose, blight (Pseu- 
domonas juglandis Pierce l ) . — 
Up to the present time this disease has occurred only 

1 Pierce, N. B., Bot. Gaz. 31, 273. 
2g 




Fig. 195. — Walnut twig blighted by 
bacteria. After R. E. Smith. 



450 DISEASES OF ECONOMIC PLANTS 

upon the Pacific coast, where it often causes a loss of 50 
per cent of the crop. 

It may be recognized as black cankered spots upon the 
young nuts, which fall prematurely, or by similar spots upon 
the young green shoots. In seasons favorable to blight 
much of the terminal growth is killed and the succeeding crop 
is thereby reduced. 




Fig. 196. — Bactsrial blight of walnuts. After R. E. Smith. 

Two treatments with Bordeaux mixture, after thorough 
removal of diseased parts, have been known to prevent 50 
per cent of the loss. x The second spraying should be 
given when the nuts are firmly set. Care should be taken 
to select resistant trees for propagation. 

WILLOW 

Tar spot (Rhytismose) . See maple. 

Rust (Melampsora saliciscaprce (Pers.) Wint.). — Of 
tree rusts this is one of the most abundant, occurring as 

1 U.S. Dept. Agr. Yearbook, p. 98, 1904. 



ORNAMENTAL PLANTS 451 

dusty yellow sori upon the lower leaf surfaces. Young trees 
are sometimes somewhat injured by it, and the trees are 
rendered unsightly, especially by the defoliation that is 
induced. In the latter part of the season the winter sori 
appear as reddish brown to black, waxy or crusty spots. 

A similar rust is common upon cottonwood, Balm of 
Gilead, poplar. 

Powdery mildew. See oak. 

Powdery mildew, uncinulose ( Uncinula Salicis (DC.) 
Wint.). — A characteristic white flour-like growth appears 
upon the leaves, usually upon both sides. In later stages 
small black perithecia are seen upon the white background. 



ORNAMENTAL PLANTS 

VARIEGATED PLANTS, IN GENERAL 

In variegated plants the non-green parts of a leaf afford 
less resistance to disease than do the green parts of the same 
leaf. It thus happens that many diseases occur upon the 
variegated species that are not found upon the usual green 
species. Variegated Aspidistra, Pelargonium, Alternanthra, 
Abutelon, Ageratum, Aralia, Begonia, Centaurea, Coleus, 
Croton, Cyclamen, Dieffenbachia, Dracaena, Euonymus, 
Ficus, Fraxinus, Funkia, Hedera, Hibiscus, Hydrangea, 
Impatiens, Maranta, Nepeta, Nerium, Pittosporium, 
Ptychosperma, Sambucus, Solanum, Sarracenia, Spiraea, 
Vinca are subject to disease caused by various species of 
Colletotrichum, Ascochyta, Phyllosticta, Glceosporium, 
Leptosphaeria, Cercospora, Septoria, Coryneum, Conio- 
thyrium, Laestadia, and Diplodia. 



452 DISEASES OF ECONOMIC PLANTS 

The number of these diseases is so large that separate 
discussion cannot be given to them. The grower should 
recognize, however, the special weakness of this type of 
plant and compensate for it by special care as to hygienic 
surroundings, clean-culture methods, and liberal use of pro- 
tective sprays when acervuli, pycnidia, or molds indicate the 
presence of a fungus. 

ASTER, CHINA 

Wilt, stem rot, fusariose 1 (Fusarium sp.). — The wilt, 
mentioned as early as 1896 by Galloway, has since been 
reported from Massachusetts and Colorado, and is probably 
the most important disease of the China aster. The time 
of transplanting the beds and blossoming time are most 
susceptible periods, though the wilt is present to some ex- 
tent at other times. 

The most conspicuous symptom is the sudden death of 
the plants, with all portions of the stem except the wood 
rotted at the ground line. Close observation earlier shows 
the leaves upon one side of the plant, particularly the lower 
leaves, yellowed and wilted, and the youngest leaves to 
be smaller than normal. The wilting effect may some- 
times be found first on one side only of one of the lower 
leaves. Plants attacked early may die, or in milder cases 
may survive to produce a few small blooms. If the 
symptoms first show at blooming time, their sequence is 
the same. 

The roots in early stages appear healthy, but the stem 
near the ground, in longitudinal section, shows darkening 
of the outer wood, local at first upon the affected side, but 

1 Smith, R. E., Mass. Agr. Exp. Sta. Bui. 79, February, 1902. 



ORNAMENTAL PLANTS 453 

extending rapidly in all directions. Eventually the dis- 
coloration extends into the bark, which rots away. 

In the seed bed the same disease may occur as damping 
off. See p. 60. It seems that the original infection 
always occurs in the seed bed, not in the open. 

Plants started in the open are not susceptible. If it is 
necessary to start them under glass, too thick sowing should 
be avoided, and they should be ventilated thoroughly. 
Soil that is known to be infected should not be used. The 
disease may be prevented by avoidance of the conditions 
that favor damping off. 

Rhizoctoniose. See carnation. 

Rust (Colceosporium sonchi (Pers.) Lev.). — Orange-red 
sori, waxy in consistency, are produced in great numbers 
upon the leaves, which when badly affected curl and die and 
thus bring about the death of the plant. 

BALM, SILVER 

Rust (Puccinia Mentha Pers.). — Some thirty species of 
members of the mint family, including peppermint, thyme, 
catnip, monarda, are affected by this rust. It is recognized 
by its sori, which are at first cinnamon-colored, later chest- 
nut-brown. Badly diseased leaves curl and die. 

Infected refuse should be burned. 

BLETIA 

Colletotrichose (Colletotrichum Bletice Halst.). — The 
leaves of this orchid are frequently disfigured by very dark, 
almost black spots. In late stages the dead tissue falls 
away, leaving merely shreds of veins traversing the place 
of disease. 



454 DISEASES OF ECONOMIC PLANTS 

The tips of the leaves are often frayed. 

Volutellose (Volutella concentrica Halst.). — Numerous 
lemon-colored acervuli surrounded by concentric bluish 
rings render these spots different from those above 
described. 

CALLA 

Soft rot, 1 bacillose (Bacillus aroidece Townsend). — A 
large annual loss and frequently the abandonment of calla 
growing is due to this disease, which is known through- 
out the United States, and which is perhaps identical with 
the carrot soft rot. 2 

The affected plants rot off near the soil surface, and the 
rot progresses from this point up into the leaves or down 
into the corm. Usually the rot first shows at the top of the 
corm, but in some instances it is seen first at the edge of a 
petiole, or on the corm below ground. 

In section the diseased portion is brown, soft, and watery. 
Leaves whose bases are diseased become pale at the edges, 
then brown. Similar changes occur in spots on the leaf, and 
the whole leaf eventually dies, or the rot may progress so 
rapidly that the leaf falls before losing its green color. 
The flower or its stalk are similarly diseased. Through 
the corm the roots are reached. Here the skin is unaffected 
and remains as a parchment-like tube filled with the creamy 
residue of decay. Rot of the bulb may be arrested by 
unfavorable conditions and show only as dark sunken spots. 

1 Townsend, C. O., U.S. Dept. Agr. Bur. Plant Indus. Bui. 60, June, 
1904. 

2 Harding, H. A., Jones, L. R., and Morse, W. J., N.Y. (Geneva) Agr. 
Exp. Sta. Tech. Bui. 11. 



ORNAMENTAL PLANTS 455 

The course of the disease extends from a few days to several 
weeks, or the disease may lie dormant for months, even 
from season to season. Such cases of dormant disease 
carry the infection to the succeeding crop and in commercial 
corms from country to country. The rot spreads rapidly 
from plant to plant by way of the diseased roots and through 
the soil itself. The causal bacillus remains in the soil and 
may attack healthy corms planted therein at later periods. 

No known treatment of diseased plants is practicable. 
Infection of soil may be prevented by careful inspection of 
all corms so as to avoid diseased ones. It is best to test 
commercial corms in pots to be assured of their healthful- 
ness before putting them in the beds. All soil from badly 
infected beds should be disinfected or removed and fresh 
soil supplied. 

Phyllostictose (Phyllosticta Richardice) Halst.). — 
Blighted leaves bear large ashen spots upon which are 
numerous minute dark pycnidia. 

Cercosporose (Cercospora Richardicecola Atk.). — 
This was first mentioned by Atkinson in 1891 as occurring 
in Alabama. The edges of the leaves turn black in circular 
spots. 

CARNATION 

Rust (Uromyces caryophyllinus (Schrk.) Schroet.). — 
The carnation rust was first described in 1789 in Germany 
and was noted in the United States by Arthur 1 in 1891, then 
evidently a quite recent importation from the mother coun- 
try. It rapidly became widespread through sale of infected 
plants and cuttings and was soon present in almost all green- 

i Arthur, J. C, Bot. Gaz. 1891. 



456 DISEASES OF ECONOMIC PLANTS 

houses. Though widely known in Europe, it did not seem 
to be especially destructive there ; but upon entrance into 
America its character changed to that of an aggressive pest, 
and ruin was brought to the beds in many greenhouses. 
The entire contents of large houses valued at thousands of 
dollars was in many instances utterly lost. After a short 
period of extreme destructiveness, which was at its height 
about 1893, the vigor of the attack waned, until to-day the 
pest does only a small fraction of the damage that was com- 
monly due to it in the early years of its invasion, though it 
is still one of the serious carnation diseases. 

The rust is easily recognized by the sori; in this case full 
of brown spores which may be rubbed out as a dark dry 
powder. The sori, at first covered by the white epidermis, 
are 1-2 mm. in diameter, round or elongated in the direction 
of the length of the stem or leaf. When very numerous, the 
affected part is slightly bleached or yellowed and appears 
swollen, owing to the much-ruptured epidermis. The my- 
celium of the causal fungus is usually general throughout 
affected plants, but may, in case of new infection, be limited 
to the immediate region of the sorus. 

There is much difference in varietal resistance, a fact that 
should receive due weight in the selection of varieties for 
culture. The William Scott is highly resistant. Uncle 
John, Daybreak, Silver Spray, and Jacqueminot are 
susceptible. 

Cuttings should never be taken from diseased stock. 
If there is doubt as to the absence of superficial spores, it is 
well to dip the cuttings in potassium sulphide, one ounce 
to one gallon. A weekly protective spray of copper sul- 
phate, one pound to twenty-five gallons, throughout the life 



ORNAMENTAL PLANTS 457 

of the plant is also recommended. The leaves should be 
kept as free from moisture as possible by free ventilation, 
and still better by subirrigation. 

Fumigation of the houses in the fall before the introduc- 
tion of the plants serves to lessen infection from old spores. 

Septoriose (Septoria Dianthi Desm.). — The spots of this 
disease — usually upon the leaves, sometimes upon the 
stems — are circular or oblong, blanched or pinkish, and 
purple bordered. Numerous small black pycnidia lie in 
the central region. The disease is especially abun- 
dant upon the lower portion of the leaves and the 
sheaths. The diseased part often becomes contracted, 
which results in bending and curling of the leaves. Sur- 
face watering of the plants or humid atmosphere tend to 
increase the trouble. 

Vermiculariose (Vermicularia subeffigurata Schw.). — The 
bases of the leaves or the stems are usually the points of 
attack. Black spore-bearing bodies appear in abundance. 
Spraying with ammoniacal copper carbonate has given 
good results. 

Alternariose (Alternaria Dianthi 1 S. & H.). — This leaf 
and stem disease has been reported as quite troublesome 
in Connecticut, Pennsylvania, District of Columbia, and 
North Carolina. It consists of spots mostly upon the 
leaves, sometimes upon the stems, especially at the nodes. 
These are strikingly characteristic, of ashen whiteness, 
with the centers occupied by an often scanty, though 
sometimes profuse, black fungous growth. The diseased 
spot is dry, somewhat shrunken, thinner than healthy 
portions of the leaf, approximately circular, though often 

1 Stevens, F. L., and Hall, J. G., Bot. Gaz. 47, 1909. 



458 



DISEASES OF ECONOMIC PLANTS 



somewhat elongated in the direction of the longitudinal 

axis of the leaf (Fig. 197). When at the node, the disease 
usually involves the bases of both of the 
leaves, as well as the stem between them. 
As these nodal spots age, the disease pene- 
trates through the stem, killing its tissue, 
which shrinks somewhat and becomes soft 
and disintegrated, resulting in the death of 
the more distal portions of the plant. 

A striking feature is the tendency of this 
disease to infect to a large degree one variety, 
the Mrs. Thomas W. Lawson, to the exemp- 
tion of others. 

Fusariose, of stems, stem rot, wilt, die back 
(Fusarium sp.). — Described in 1897 by Ster- 
gis, this rot occurs chiefly upon the stems 1 
and larger branches, discoloring the wood and 
killing the bark, but rarely causing soft rot. 
The diseased plants die gradually with yellow- 
ing and drying of the foliage, much as though 
due to insufficient water supply. 

When practicable, beds should be disin- 
fected and new uninfected stock introduced. 
The disease when first introduced upon a 
few plants can be stopped by the immediate 
removal and destruction by fire of the dis- 
eased plants. 
Fusariose, of leaves, leaf spot (Fusarium sp.). — This is 

a secondary disease following primary lesions of the rust. 

The spots as described by Stewart 2 vary from 3-25 mm. in 

1 Stewart, F. C., Bot. Gaz. 27, 129, February, 1899. 

2 Stewart, F. C, N.Y. (Geneva) Agr. Exp. Sta. Bui. 164, 1899. 



Fig. 197. — 
Carnation leaf 
showing spot 
caused by Al- 
ternaria Dian- 
thi. Original. 



ORNAMENTAL PLANTS 459 

length; are elliptical in outline ; covered with a pinkish gray 
mold ; irregularly dotted near the center with light yellow 
spore masses. This is not common and may be 
prevented by avoidance of the rust. 

Volutellose (Volutella Dianthi Atk.). — The 
affected parts are pale and studded with mi- 
nute black acervuli. This disease is of greatest 
injury in the cutting bench. 

Heterosporiose, leaf mold (Heterosporium 
echinulatum (Berk.) Cke.). — Circular spots, 1-4 
mm. in diameter, bearing more or less concentric 
zones of dark mold, appear upon the leaves, 
especially the younger ones, also upon the stems 
and sometimes upon the calyx. When upon the 
calyx, deformation of the flower results. In some 
instances the whole top of a plant becomes moldy. 

Infected refuse and leaves should be burned and 
Bordeaux mixture employed as a spray. 

Bacterial spot (Bacteria). — The spots of the 
leaves and stems are described by Woods 1 as 
small, usually surrounded by a narrow water- 
soaked area, while the center is commonly slightly 
brown. As the spots grow larger they resemble FlG 198 __ 
septoriose spots with the exception of the water- Carnation 
soaked margin. Later they dry and collapse. foiiowSg 
Badly diseased leaves wither. In some cases rust. Af- 
nearly all the leaves on many of the stems are ^ stew " 
so badly diseased as to be hopeless. 

This trouble can be checked by removing and burning 
all diseased leaves, then spraying with formalin, 1 part to 

1 Woods, A. F., Sci. n. s. 18, 537, October 23, 1903. 



460 DISEASES OF ECONOMIC PLANTS 

500. This should be clone before noon, so that the plants 
may dry before night. 

Botryose (Botrytis sp.). — A brown mold similar to that 
upon lettuce sometimes attacks the carnation bud, rotting 
it before it opens. 

The only remedy available is to burn all infected refuse 
and to give thorough ventilation. 

Bud rot, sporotrichose (Sporotrichum anthophilum Peck). 
— In this malady some buds never open, others fail to ex- 
pand to perfect flowers, still others deviate only slightly 
from the normal. Badly affected flowers, if not picked, 
wither and turn brown, — first the petals, then the sepals. 
All parts of the flower within the calyx are eventually 
affected with a rot, and in some cases, though not always, 
hyphse of the causal fungus may be seen with the naked 
eye. Mites are usually present, but they are not the true 
cause of the disease. 

Neglect is among the prominent predisposing causes, 
especially the presence of too much water in the soil or air, 
and the accumulation of debris, leaves, trimmings, and other 
organic matter on the benches. 

The Lawson and Queen Louise are mentioned as especially 
susceptible. 1 

The disease may cause considerable damage; thus a 
daily loss of from $1.50 to $2 is recorded in one small 
house. Since the buds only are affected, not the plants 
themselves, no permanent injury is done, and clean culture, 
destruction of all refuse which might harbor the fungus, 
maintenance of the moisture at the minimum, and the pick- 
ing and burning of all infected buds will soon bring relief. 
1 Heald, F. D., Neb. Agr. Exp. Sta. Bui. 103. 



ORNAMENTAL PLANTS 461 

Rhizoctoniose, stem rot (Rhizodonia sp.). — The plants 
suddenly wilt, dry, and die, while the outer portion of 
the stem becomes soft and rotten. Sclerotia as described 
for the potato are present. For further discussion of stem 
rot, see p. 61. 

CHRYSANTHEMUM 

Septoriose, leaf spot (Septoria chrysanthemi Allesch.). — 
Large brown to black blotches, often irregularly circular 
and of indefinite border, appear upon the leaves. These 
enlarge and coalesce to involve the whole leaf, which 
withers, dies, and falls away. 

The lower leaves are first affected, but in later stages all 
the leaves of the plant maybe badly spotted, and practically 
complete defoliation may result. Cuttings from infected 
stock should be avoided. All diseased foliage should be 
picked, collected, and burned, and the remaining foliage 
should be sprayed with Bordeaux mixture with soap added 
sufficient to form a suds to increase its adhesive power. 
Five or six sprays during the season are usually sufficient. 1 

Phyllostictose (Phillosticta sp.). — This disease, first de- 
scribed in 1893, is very similar to the above, except that 
the spots are more regularly circular, are purplish brown, 
and with a distinct border. Pycnidia which may often 
be seen with the naked eye are present. 

Rust (Puccinia chrysanthemi Roze) . — Apparently a 
native of Japan, the rust was introduced into England 
(1895) and Europe through commercial agencies, 2 and 
similarly into the United States, where it was first noted 

1 Beach, S. A., N.Y. (Geneva) Agr. Exp. Sta. Rpt. 1892, p. 557. 

2 Arthur, J. C, Ind. Agr. Exp. Sta, Bui. 85, p. 150, October, 1900. 



462 



DISEASES OF ECONOMIC PLANTS 



in 1896 in Massachusetts. It was rapidly spread through- 
out this country by diseased stock, and is now known 
in nearly all localities where the chrysanthemum is culti- 
vated. The loss occasioned by the diminution in vigor 
of the plant and consequent imperfection of blooms is 

large. 

The sori, 2-3 mm. in di- 
ameter, which are diagnostic, 
first appear as small blisters 
covered by the epidermis. 
The rupture of this covering 
discloses a dark brown mass 
of spores. The sori are usu- 
ally very numerous upon the 
lower leaf surface, less abun- 
dant above, and the spores as 
liberated form dusty coatings 
upon the leaves. Badly af- 
fected leaves curl, shrivel, and 
die. The plants are dwarfed 
and fail to produce flowers of 
value. 
All new stock introduced to the houses should be care- 
fully inspected and all diseased stock destroyed by fire. 
New stock should be isolated and watched for a month or 
more to be sure that no rust develops. If disease appears, 
all affected leaves should be picked and burned with pre- 
cautions to avoid scattering the spores. If the rust con- 
tinues to appear, all aboveground parts must be destroyed 
by fire at the end of the season, and plants for the next year 
raised in uncontaminated soil and house. 




Fig. 199. — Chrysanthemum leaf show 
ing rust sori. Original. 



ORNAMENTAL PLANTS 



463 



Ascochytose, ray blight (Ascochyta chrysanthemi Stevens). 

— In this disease, described by Stevens 1 as doing consider- 
able damage in North Caro- 
lina, the ray flowers are 
blighted, resulting in im- 
perfect opening of the buds. 
Thorough spraying with 
Bordeaux mixture from the 
beginning of the season un- 
til blossoming, accompanied 
by destruction of infected 
refuse, has proved a satis- 
factory treatment. 

Powdery mildew (Oidium 
chrysanthemi Rbh. of Ery- 
siphe cichoracearum DC). 

— This mildew occurs as 
white, flour-like spots upon 
the green parts of the plant. 
It is not often serious, but 
if it should be, can probably 
readily be controlled by the 
means suggested for grape 
oidiose. 

Cylindrosporiose (Cylin- 
drosporium chrysanthemi 

Ell. & Dearn). — First described in 1893, this closely re- 
sembles septoriose, though it develops somewhat more 
rapidly and is consequently more injurious. Often the 
leaves die and flowers fail to form. Treatment is the same 
as for septoriose. 

1 Stevens, F. L., Bot. Gaz. U, 241, October, 1907. 




Fig. 200. — Chrysanthemum blossom dis- 
torted with ray blight. Original. 



464 DISEASES OE ECONOMIC PLANTS 

Pseudomonose, tumor, gall (Pseudomonas tumefaciens 
Smith & Townsend). — Galls upon the stems of this 
plant have been proved by Smith and Townsend 1 to be 
due to a species of Pseudomonas. Treatment has not yet 
been discussed. 

CLEMATIS 

Phomose (Phoma sp.). — Plants affected with this disease 
were first noted in 1883. 2 They showed roots which were 
rotted for several centimeters distant from the stem. 
Minute black pycnidia occurred upon the affected, parts. 

COREOPSIS 
Rhizoctonia. Seep. 61. 

COSMOS 

Phlyctaenose (Phlyctcena sp.). — The first indication of 
disease is seen in brown discoloration of the stem or 
branches, the attack often, though not always, occurring 
at a wound. The diseased branches at the point of at- 
tack are weak and frequently break off. Minute pycnidia 
are present in the diseased parts. 

CYCLAMEN 

Phomose (Phoma cyclamence Halst.). — A disease of the 
foliage which sometimes causes almost entire loss of the 
crop is marked by large, dark, irregularly shaped spots 
upon the leaf. These spots later dry, turn lighter in 
color, and show a series of concentric light and dark 

1 Smith, E. F., and Townsend, C. O., Centbl. Bakt.££, 89, December, 
1907. 

2 Arthur, J. C, N.Y. (Geneva) Agr. Exp. Sta. Rpt. 3, p. 383, 1884. 



ORNAMENTAL PLANTS 465 

bands, at the same time becoming brittle and often 
breaking away. Diseased leaves should be burned and 
the plants sprayed with Bordeaux mixture or ammoniacal 
copper carbonate. 

Glomerellose (Glomerella rufomaculans (Berk.) Spaul. & 
von Schrenk var. cyclaminis Patt. & Ch.). 1 — The spots on 
the leaves are circular, watery, with definite borders. Black 
hairy acervuli are often present in great numbers. 

DAHLIA 

Powdery mildew (Oidium of Erysiphe communis Wallr.). 
— This powdery mildew is quite common, affecting par- 
ticularly the lower leaves late in the season. 

Phomose ' (Phoma Dahlia? Berk.). — The stems of the 
flowers are the chief seats of attack. The flowers are 
small and are often dropped before opening. 

DRACAENA 

Phyllostictose (Phyllosticta maculicola Halst.). — This 
may be recognized as small, brown, somewhat angular 
spots on the leaves, each spot surrounded by a rather 
wide yellow border. Minute pycnidia are present. 

FERNS 

Phyllostictose, blight (Phyllosticta pteridis Halst.). — The 
tender growing tips of ferns are subject to blight, and 
blighted spots may also occur lower upon the leaf. The 
brown dead tips and leaf spots bear minute pycnidia. 
Blighted parts should be cut away and burned and the 

1 Patterson, Mrs. Flora, and Charles, Vera K., U.S. Dept. Agr. Bur. 
Plant Indus. Bui. 171. 
2h 



466 DISEASES OF ECONOMIC PLANTS 

remaining foliage sprayed with Bordeaux mixture. The 
disease is strictly local, and close attention will stop its 
spread, even after it has attained considerable foothold. 

Completoriose (Completoria complens Lohde). — Upon 
sporelings (prothallia of aspidium and pteris) this dis- 
ease is first shown by a yellow or yellow-brown color, 
as seen in mass. Under a hand lens the abnormal color is 
seen as spots, varying from green to yellowish brown and 
later to black. In later stages disintegration of the af- 
fected cells gives the prothallia a ragged appearance. 

GOLDEN GLOW 

Powdery mildew (Erysiphe cichoracearum DC). — This 
is a characteristic powdery mildew. 

HOLLYHOCK 

Rust (Puccinia Malvacearum Mont.). — This rust, native 
to Chili, was introduced into France about 1868. It 
spread rapidly over all Europe, from whence it came to the 
United States about 1886 upon infected seed. It was 
rapidly disseminated throughout this country, and is 
now known from Maine to Louisiana, in many places 
rendering the plants unsightly. It is easily recognized by 
its yellow to brown sori, each sorus considerably raised 
above the surface of the leaf or stem as a small, wartlike 
protuberance. Badly rusted leaves, or even whole plants, 
wither and die as though blighted. In mild cases the 
leaves remain green and the plant may bloom. 

It is recommended to sponge the diseased parts with 
permanganate of potash: two tablespoonfuls of saturated 
solution diluted with one quart of water. 



• OBNAMENTAL PLANTS 467 

Cercosporose (Cercospora althceina Sacc). — Upon the 
leaves and other green parts of the hollyhock, velvet leaf, 
and mallow rather large, dark, angular spots are produced 
in abundance, each spot with a dark border and an ashen 
center upon which numerous black hyphse may be seen. 
Badly diseased leaves fall, and by midsummer only dead, 
leafless stalks may remain. Even in mild cases, by de- 
creasing the amount of green surface, the spots both injure 
the appearance of the plant and lessen productiveness. 

Spraying with Bordeaux mixture or ammoniacal copper 
carbonate at intervals of about ten days is thoroughly 
effective. 

Phyllostictose (Phyllosticta althceina Sacc). — This pest, 
long known in Europe, is recognized as large, brown, 
circular spots, 1-2 cm. or more in diameter, upon the 
leaves. The centers are brittle and usually break away 
irregularly. 

Colletotrichose, anthracnose (Colletotrichum Malvarum 
(Br. & Casp.) South.). — Since about 1885, this disease has 
been noticed in destructive form in greenhouses, particu- 
larly in the propagating beds; in some cases to such serious 
extent as to nearly prohibit commercial culture of the 
hollyhock. 

It occurs upon any green part of the plant. On the leaves 
it forms brown spots and causes withering. When upon 
young succulent petioles or stems, collapse of the parts be- 
yond follows. If the parts be older, sunken spots varying 
from light yellow to black are produced. 

The plants should be sprayed with Bordeaux mixture as 
soon as the first leaves appear and every second day there- 
after. 



168 DISEASES OF ECONOMIC PLANTS 

HYDRANGEA 

Phyllostictose (Phyllostida Hydrangece Ell. & Ev.). — ■ 
Large rusty brown blotches occur upon the leaves, in 
some cases to such extent that the tops of the plants must 
be cut away, to the entire destruction of their decorative 
value. 

Cercosporose (Cercospora sp.). — Small, round or angular 
white spots with a very small amount of dark hyphal 
growth in the centers are common upon this plant. The 
spots are definite and are bordered by a narrow reddish 
purple line. 

IVY (Hedera) 

Vermiculariose {V ermicularia trichella Ft.). — This blight 
usually begins midway between base and apex of the 
leaf, and is especially common upon the white portions of 
the variegated varieties. The diseased portions turn black, 
and small black acervuli appear. 

LILAC 

Powdery mildew (Microsphcera alni Wallr.). — The char- 
acteristic spots of the powdery mildew, white and flour-like, 
are frequent upon the lilac. Black perithecia are abundant 
late in the season. 

LILY 

Botryose (Botrytis sp.). — This exceedingly destructive 
mold of the lily was noted about 1885, and was first 
closely studied by Ward 1 in 1888. It makes its appear- 

1 Ward, H. M., Ann. Bot. II, No. 7, November, 1888. 



OBNAMENTAL PLANTS 469 

ance in the spring as small, orange-colored spots upon the 
leaves and buds. These enlarge, and later become coated 
with a light brown, dusty, fuzzy mold which destroys the 
leaves and blossoms, often leaving only the naked stalks 
standing. 

Sclerotia much like those described under lettuce sclero- 
tiniose appear in association with the decay in its late 
stages. Their subsequent history is like that of lettuce 
sclerotia. 

MIGNONETTE 

Cercosporose (Cercospora Resedce Fckl.). — This disease 
occasionally ruins the greenhouse crop. The spots are 
at first minute, pale, with brownish or yellowish borders, or 
they spread over the leaf as a reddish discoloration. In 
late stages they are uniform brown, with dark hyphse 
scattered over the central portions. The dead areas 
enlarge irregularly, and the leaves finally curl and die. 

Bordeaux mixture or ammoniacal copper carbonate, used 
once a week, have proved effective remedies. 

NASTURTIUM 

Pseudomonose (Pseudomonas sp.). — In this disease the 
leaves are wilted and bear water-soaked spots 3-5 mm. 
in diameter or larger. 

Alternariose (Alternaria of Pleospora Tropceoli Halst.). — 
The leaves which are affected turn fight green, later 
yellow, and still later are covered with a black mold. 

Damping off {Colletotrichum sp.). — Damping off due to 
a species of colletotrichum is common in the cutting bed. 
The diseased parts bear numerous black acervuli. 



470 DISEASES OF ECONOMIC PLANTS 

OLEANDER 

Bacillose, knot, gall (Bacillus). — This disease both upon 
leaves and stems appears to be identical with that upon 
the olive. 1 Smith of California believes it to be caused by 
the same germ as that upon the olive, while E. F. Smith 
thinks it is different. 

ORCHIDS 

Botryose (Botrytis vulgaris Ft.). — The plants are often 
rendered unsightly and the flowers valueless by straw-col- 
ored spots. They are at first very minute, but enlarge 
rapidly and involve large areas. A gray mold similar to 
that found upon the lily appears later. 

All infected refuse should be burned. 

PALM 

Colletotrichose (Cottetotrichum sp.). — Palms often die 
and turn black at the tips of the leaf segments, or similar 
spots may appear upon other parts of the leaf. These 
spots near their edges have a watery appearance. When 
they become dry, purplish acervuli appear. Upon seed- 
lings the disease is particularly troublesome, resulting in 
failure of the leaves to unfold. 

The blighted parts should be cut away and burned and the 
remaining foliage sprayed at least once each week with 
Bordeaux mixture or ammoniacal copper carbonate. 

PANSY 

Colletotrichose (Cottetotrichum violo3-tricoloris R. E. 
Smith) . — This blight has been noted in many states. It is 

1 Smith, C. M Bot. Gaz. 42, 301, October, 1906. 



ORNAMENTAL PLANTS 471 

characterized by the appearance of dead, black-bordered 
spots on the leaves and petals, 1 thus disfiguring the flowers, 
and affecting the production of seed, or even bringing pre- 
mature death to the plant. 

Thorough and frequent spraying with Bordeaux mixture 
is advocated. 

Fusariose (Fusarium violce Wolf 2 ) . — This was noted 
as of economic importance in Nebraska, where it caused 
sudden dying of the plants, apparently healthy plants 
becoming dry and dead in a few days. Slight sunken 
areas were evident on the stems just above the ground, and 
the roots were reduced to mere stumps. 

Rust (Puccinia Violce (Schum.) DC). — One of the 
most common of pansy diseases is this true rust which 
affects all aerial parts of the plant. It is recognized by 
its sori. 

Downey mildew. See violet. 

PEONY 

Botryose (Botrytis peonice Oud.). — This mold was first 
noted in 1897 in Europe. It has since been mentioned 3 
in Canada, Massachusetts, Rhode Island, Pennsylvania, 
and Maryland as causing serious loss. 

The plants are attached almost as soon as they appear 
above ground, and ashen gray spots are produced both 
upon the bud, scales, and stems. Brown mold similar to 
that described for lettuce often, but not always, develops 

1 Smith, R. E., Bot. Gaz. 27, 203, March, 1899. 

2 Wolf, F. A., Mycologia 2, 19, January, 1910. 

3 Patterson, Mrs. Flora, and Charles, Vera K., U.S. Dept. Agr. Bur. 
Plant Indus. Bui. 171. 



472 DISEASES OF ECONOMIC PLANTS 

upon the affected parts. Numerous greenish black, flat 
sclerotia, 1-1^ mm. in diameter, are formed in the stems. 
Dead leaf and stem remains should be removed from the 
peonies before they are set in the ground. Bordeaux mix- 
ture may be used after the plants appear in the spring. 
Infected beds should be steamed. 

PINK 

Rust (Puccinia Arenarice (Schum.) Schroet.). — This 
rust was described in 1803 by Schumacher. It is quite 
common upon various members of the pink family, as chick- 
weeds, corn cockle, bouncing bet, etc. The sori are large 
raised blisters arranged in characteristic concentric circles. 

Diseased plants should be burned. 

PRIMROSE 

Phyllostictose (Phyllosticta primulicola Desm.). — Large, 
circular, brown dead spots are produced upon the leaves. 
Minute dark pycnidia may be seen. 

Ascochytose (Ascochyta primulce Trail). — Well-defined 
oval spots, resembling those of phyllostictose, are formed. 
These two diseases cannot be distinguished without the 
aid of the microscope. 

Ramulariose (Ramularia primulce Thuem.). — In this 
disease the blotches are yellow with centers of ashen 
whiteness. No pycnidia are present, but instead a gray 
coating of mold. 

Colletotrichose (Colletotrichum primulce Halst.). — In this 
blight the leaf as a whole is more involved than in the 
above diseases, and definite spots are more rare. Dark 
acervuli are present. 



ORNAMENTAL PLANTS 473 

Botryose (Botrytis vulgaris Fr.). — This occurs upon leaves 
and flowers much as upon lettuce. 

Bordeaux mixture is useful with all of these Primrose 
diseases. 

PRIVET 

Gloeosporiose, anthracnose (Glceosporium cingulatum 1 
Atk.). — Twig blight superficially resembling that of the 
pear is a character of this disease in its later stages, terminal 
parts of the twigs 2-5 cm. long being affected. The line of 
separation between diseased and healthy tissue is a sharp 
one through shrinking and depression of the diseased part. 
In early stages depressed oblong diseased spots, at first very 
minute, are seen upon the bark. These spots enlarge, 
eventually girdle the twig, and cause the death of the distal 
part. Minute black elevated acervuli, visible to the naked 
eye, are scattered over the surface of the original disease 
spots. 

Affected branches should be cut well below the disease 
and burned. A spring spraying, before the buds swell, 
with any good dormant spray will still further reduce infec- 
tion. 

ROSE 

Black spot (Adinonema Rosce (Lib.) Fr.). — Both in and 
out of doors, this is a widely known and destructive rose 
disease. It was first described in 1826, and is now known 
throughout Europe and the United States. It consists of 
irregular circular or oval indefinitely bordered black spots 
upon the upper surface of the leaves that are mature or 

1 Atkinson, G. F., N.Y. (Cornell) Agr. Exp. Sta. Bui. 49. 



474 



DISEASES OF ECONOMIC PLANTS 



nearly so. The larger spots are a centimeter or more in 
diameter, and they frequently coalesce so as to nearly 
cover whole leaflets. 

With age the spots turn gray at the centers, at which part 
the leaf dies. They also become more regular in outline 




Fig. 201. — Rose mildew ; diseased and healthy shoots. Original. 



than in their earlier stages. Portions of the leaflets out- 
side of the area actually spotted often turn yellow, and the 
diseased leaflets fall off prematurely. Thus the beds be- 
neath diseased plants are often strewn with fallen leaves. 
All infective material should be gathered and burned, and 
both bushes and ground be well cleared of superficial spores 



ORNAMENTAL PLANTS 475 

by a good dormant spray. Ammoniacal copper carbonate 
used once each week is effective after the plants are in foli- 
age. 

Powdery mildew (Sphcerotheca pannosa (Wallr.) Lev.). — 
This is perhaps the most widespread and destructive of all 
rose diseases both under glass and in the open, being es- 
pecially destructive to the Rambler varieties. In mild cases 
it occurs merely as flour-like, dusty white patches upon the 
leaves. But when present, it usually becomes aggressive, 
attacking the young leaves and tender shoots, which 
become dwarfed, curled, reddened, variously deformed (Fig. 
201), and covered with the white powder of spores and 
spore stalks. The vitality of the plant is so lowered by 
repeated attacks and even by direct attack upon the buds 
that the plants become worthless. 

Indoors sulphur is serviceable. The house should be 
closed and the sulphur boiled in a kettle for two to three 
hours twice weekly, or the house may be closed in the morn- 
ing, the temperature raised to 75° F., and the air well filled 
with sulphur from bellows. The temperature should then 
be raised to 85°-90° F., and then allowed to cool gradually. 

Either out doors or in, spraying with any good fungicide, 
as potassium sulphide, 1 ounce to 2 gallons, or Bordeaux 
mixture, is effective. 

Rust (Phragmidium subcorticum (Schrank) Wint.). — 
This true rust is common in Europe, and is found in many 
parts of the United States from the Atlantic to the Pacific ; 
still it is not a very common pest. 

Early in the season orange-yellow sori appear upon the 
green parts of the plant : on the leaf as small, circular spots ; 
on the stems and petioles often as quite large, powdery 



476 DISEASES OF ECONOMIC PLANTS 

masses. Later in the season the color of the sori changes 
to brick red. 

Affected branches should be promptly burned, and all 
infective material should be burned in the autumn. If 
the disease reappears, the whole plant should be dug up 
and burned. In beds where the disease has occurred, a 
dormant spray should be applied in early spring. 

Rust (Phragmidium speciosumFr.). — Though much like 
the last, this disease is limited to the stems, rarely petioles, 
in its attack. The sori are irregular and black. Since 
the causal fungus is perennial in the stems, excision and 
burning are to be practiced. 

Gloesporiose, anthracnose (Glceosporium Rosce Halst.). — 
This anthracnose is very similar to that of the raspberry. 
The diseased canes, bearing small, pale leaves, die from the 
tip backward for 2-3 dm., and red acervuli appear upon them 
after death. Often the canes become completely defoliated. 

Affected plants should be sprayed with Bordeaux mix- 
ture or ammoniacal copper carbonate. 

Sphaerellose (Sphcerella rosigena Ell. & Ev.). — The 
leaves are marked with gray, irregular, indefinite blotches 
which bear minute black perithecia in their centers. 

Leaf spot, cercosporose (Cercospora roscticola Pass.). — 
Circular gray spots bordered with dark purple but with- 
out pycnidia are present. 

Downy mildew (Peronospora sparsa Berk.). — This 
mildew is kin to that .of the grape. Its spots are indefinite, 
and the characteristic downy white to purple coating 
is noted upon the lower surfaces of the leaves. It is not 
common in America. 

Crown gall. See peach. 



ORNAMENTAL PLANTS 477 

SEDUM 

Septoriose (Septoria Sedi WestcL). — Dark, circular 
blotches appear upon the leaves and result in such 
defoliation that the stems often become naked nearly to 
the tips of the branches. 

Infected parts should be burned. 

Vermiculariose (Vermicularia Telephii Karst.). — This 
disease usually appears first at the point of attach- 
ment of the leaves, and later it passes to the stem, causing 
soft rot and shrinking of the outer parts. After defolia- 
tion the disease spreads slowly toward the base of the 
stem. 

Infected parts should be burned. 

SNAPDRAGON 

Colletotrichose, anthracnose (Colletotrichum antirrhini 
Stew.). — This disease which often ruins the crop is the most 
destructive of this host, both under glass and in the open. 
It attacks plants of any age, producing on the stem ellip- 
tical sunken spots, 5-8 mm. long, and on the leaves circular 
dead spots. These are at first dirty white with narrow 
brown margin ; later acervuli appear in the center, at first 
brown, then black. Diseased plants show numerous dead 
hanging leaves. The stems or lateral shoots may be 
girdled, killing the parts beyond. 

It is recommended to use only healthy plants for cuttings 
and to clean up and burn all diseased refuse. The cuttings 
should be sprayed as soon as well rooted and repeatedly 
until transplanted. Excess of water should be avoided 
and thorough ventilation provided. 

Phomose (Phoma sp.). — This is a disease of sue- 



478 DISEASES OF ECONOMIC PLANTS 

culent shoots, causing several centimeters of the terminal 
portions to wilt and die. 

Bordeaux mixture is recommended. 

SPURGE 

Gloeosporiose (Glwosporium euphorbice Halst."). — The 
attack usually begins upon the flower cluster and passes 
down the stem to the leaves, which then fall away* leaving 
the naked, blighted branches. The disease often interferes 
seriously with the ornamental effect of this decorative 
plant. 

SUNFLOWER, ARTICHOKE 

Rust (Puccinia Helianthi Schw.). — Both wild and cul- 
tivated species of sunflowers are often badly rusted. The 
early sori are yellow to brown, the later black. Badly 
rusted leaves die, curl, or fall, and much injury follows both 
to flower and seed. 

In the spring the cluster-cup stage is sometimes found 
upon the same host. There is some doubt as to the ability 
of the rust upon one species to infect all of the other species 
of host. 

Burning of infected refuse is the only remedy known. 

VERBENA 

Powdery mildew (Erysiphe dehor ucearum DC). — 
Powdery mildew is quite common upon verbena under 
glass or in the open. 

The use of potassium sulphide, 1 ounce to 3 gallons, twice 
a week has proved effective. 



ORNAMENTAL PLANTS 479 

VIOLET 

Alternariose, spot disease 1 (Alternaria Violce Galloway & 
Dorsett). — This is one of the most widespread and de- 
structive of violet diseases. It attacks the plant at any 
stage of its growth and upon any green part, but is most 
destructive upon the foliage. It first appears as small, 
definite, circular, greenish or yellowish-white spots, varying 
from mere dots to 1 mm. in diameter. The light center is 
surrounded by a narrow ring, usually dark brown to black, 
but turning lighter with age. As the spot enlarges the 
freshly diseased tissue is usually watery and translucent, 
and the center changes to yellow or gray- white and may 
fall out. Frequently by the combined effects of several 
spots the whole leaf is destroyed. If the air is damp, a 
thin coating of rusty-colored spores may be seen in the old 
spots. 

Damp, warm, cloudy, summer weather, unclean houses, 
weak plants, poor stock, poor beds, are predisposing con- 
ditions to disease. 

The Marie Louise is especially susceptible; the Lady 
Hume Campbell much more resistant. 

To avoid the disease the houses should be kept scrupu- 
lously clean, only strong stock used, infected material 
picked and burned, and insects banished. Close attention 
must also be given to ventilation, heating, shading, and 
watering. The soil should be removed each season and 
every means used to produce strong resistant plants. 

Cercosporose, leaf spot (Cercospora Violce Sacc). — 
Large dead ashen gray definite spots are produced upon 

1 Dorsett, P. H., U.S. Dept. Agr. Div. Veg. Phys. & Path. 23, No- 
vember, 1900. 




Fig. 202. — Violet leaves, healthy and affected by alternariose. After Dorsett. 



ORNAMENTAL PLANTS 481 

the leaves. No pycnidia are present, but the centers of the 
spots are darkened by the presence of hyphse. 

Phyllostictose (Phyllosticta Violce Desm.). — Straw-col- 
ored or white, circular spots about 3 mm. in diameter, 
similar to the last except for the presence of pycnidia, 
are produced upon the leaves. 

Downy mildew (Peronospora Violce DeBy.). — The downy 
mildew is in general character like that of the grape. The 
spots are indefinite, and affected plants droop and die. 

Gloeosporiose, anthracnose (Glceosporium Violce B. & Br.). 
— The anthracnose often begins at the edge of the leaf, as 
an irregular discoloration which extends inward, eventually 
blighting the whole leaf. 

Thielaviose (Thielavia basicola (B. & Br.) Zopf.). — 
Affected plants are stunted and yellow. The underground 
parts show numerous dark spots of dead tissue which often 
involve the roots for considerable distances. The disease 
is the same as that of tobacco. 

Marsoniose, leaf spot (Marsonia Violce (Pass.) Sacc). — 
This disease seems to be rare. The spots are smaller 
than with other diseases, usually only 2-3 mm. in diameter, 
and are reddish. When abundant, they cause yellowing 
of the intervening tissue and result in serious injury to the 
leaves. 

Rhizoctoniose. See p. 61. 

Zygodesmose (Zygoclesmus albidus ~Ell. & Halst.). — This 
mold forms a white, flour-like coat over the leaf. 

VIRGINIA CREEPER 

Phyllostictose (Phyllosticta ampelopsidis E. & M.). — 
The spots occurring upon the leaves and shoots are iden- 
2 1 



482 DISEASES OF ECONOMIC PLANTS 

tical in appearance with those upon the grape, and the same 
treatment is recommended. 
Powdery mildew. See grape. 

WATER LILY 

Cercosporose (Cercospora). — Circular spots, at first pale 
green, later yellow, and finally brown and dead, are produced 
upon the leaves. The dead tissue may break away, leaving 
irregular holes. 

Soda Bordeaux mixture is recommended, since it is 
effective and does not spot the leaves. It is beneficial also 
in removing undesired algal growth. 



APPENDIX 



PHYSIOLOGICAL 



The ordinary cultivated plants, all except the mushrooms, 
absorb water and all needed nutrients, except carbon, through 
the roots. The absorbing organs are very fine 
root hairs (Fig. 203), located near the extreme 
root tip. From the point of absorption the 
crude foods must be distributed to the plant 
parts where they are to be utilized; that is, 
largely to the parts that are growing and to any 
i;reen part. This necessitates a conducting sys- 
tem which exists in the veins continuous through- 
out the plant, consisting of microscopic water 
ducts (Fig. 206) extending through the wood of 
the root, stem, and leaf. The upward sap cur- 
rent passes through these ducts. A living plant 
is constantly giving off water, transpiring. . The 
amount is considerable, averaging 75 kilo, daily 
for a full size beech tree. This water too must 
rise through the ducts. 

Any injury of the root hairs retards absorp- 
tion, and any stoppage or interruption of the 
ducts in root or stem hinders the rise of sap, 
and in either case poor nutrition or even wilting 
may result. 

The carbon necessary for the plant is derived from the air, 
aken in mainly through the stomata (Fig. 205, epidermal 

483 




Fig. 203. — Plant- 
let showing lo- 
cation of root 
hairs near the 
root tip. 



484 



DISEASES OF ECONOMIC PLANTS 



pores) and elaborated under the influence of sunlight and by 
the aid of the green substance (chlorophyll) into sugar or starch, 
^ two of the fundamental 

substances upon which 
plant growth depends. 
Any injury or diminu- 
tion of the green plant 
part results at once in 
diminished carbon as- 
similation (photosynthe- 
sis) and as a consequence 
in lessened growth. Ab- 
straction of elaborated 
carbon or other useful 
substances by parasites 
is of course detrimental. 
The starch or sugar made 
in the green parts is 
needed in any growing 
part, especially in the 
roots where none is made. 
This necessitates root- 
ward conduction, which 
occurs through the bark 
or through the bark por- 
tion (phloem) of a vein 
(Fig. 206). Injury to 
the bark thus results in 
stoppage of the downward sap movement and in retarded root 
growth. 

Gaseous absorption (oxygen and carbon- dioxide) is chiefly 
through the stomata of the leaves and enlarged stomata (lenti- 
cels) of the bark. Clogging of these openings as by dust, over- 
growth by fungi or lichens, etc., interferes with this function. 




Fig. 204. — Experiment showing ascent of sap 
current through wood. Bark removed does 
not cause the leaves to wither beyond. From 
Str as burger's textbook. 



APPENDIX 



485 



The chief points of 
growth are the tips of 
the roots and branches 
and the delicate sappy 
layer between the bark 
and the wood (cambium, 
Fig. 206). Injury to 
any of these stops or 
deranges growth at the 
point injured. It is 
chiefly through derange- 
ment of some of these 
functions, absorption, 

liquid or gaseous, conduction, photosynthesis, or growth, that 
disease is caused. 




Fig. 205. — Stomata or breathing pores in the 
epidermis. From Strasburger's textbook. 




Fig. 206. — Diagram of cross section of stem 
showing circle of veins, m, pith ; i. f. c, 
cambium ring. The portion of the vein 
inside the ring is the wood and contains 
large ducts. The portion outside of cam- 
bium ring is the bark. From Strasburger's 
textbook. 



486 DISEASES OF ECONOMIC PLANTS 



FUNGI AND BACTERIA 

Fungi and bacteria are devoid of chlorophyll, therefore they 
cannot utilize the carbon of the air and are dependent, for their 
carbon supply, upon this element as elaborated by some other 
organism. When they take this food (often other nutrients as 
well) from living plants or animals, they become parasites, and if 



Fig. 207. — Apple cells invaded by the mycelium of Volutella. 
Original. 

their thievery becomes considerable, a condition of disease is pro- 
duced. By growing in the plant body they may also derange the 
vital functions in many ways. The fungous plant pathogens 
usually consist of a threadlike body (the mycelium, Fig. 207), 
which grows within or upon the plant. Masses of mycelial 
threads may be large enough to be visible to the naked eye. 



APPENDIX 



487 



The mycelium may propa- 
gate only vegetatively, often 
forming dense masses (scle- 
rotia) (Fig. 208), to tide over 
unfavorable times, or they 
may produce reproductive 
cells (spores) having the func- 
tion of seeds. The forms of 
spores and the ways in which 
they are borne are manifold 
and serve as the chief means 
of distinguishing one fungus 
from another. Some are 
borne in sacs (asci, Fig. 209); 
others on basidia (Fig. 210). 
The asci may be in perithecia (Fig. 209), or uncovered. Basidia 
are often borne upon the surface of the gills of toadstool-like 
fungi (Fig. 184), or upon the lining of the pores of similar struc- 




Fig. 208. — Sclerotia of lettuce sclerotini- 
ose, natural size. Original. 



ascospore 
Wgerm/naf/o/r 




Fig. 209. — Perithecium with asci. 




Fig. 210. — Russula rubra. Portion of the hymenium. sh, sub-hymenial laye 
b, basidia; s, sterigmata; sp, spores; p, paraphyses; c, a cystid (x 540). 




Fig. 211. — Fomes fomentarius; sporophore showing pores. After Atkinson. 



APPENDIX 



489 



tures (Fig. 211). Other spores (conidia) are borne upon the 
ends of stalks (Fig. 212). These stalks may be uncovered, 
naked, or they may be inclosed in pycnidia (Fig. 213). Several 
spore forms may be borne by one and the same fungus. The 
mode of spore formation, the time and place, are important to 




Fig. 212. — Conidia 
and conidiophore 
of powdery mil- 
dew. 



Fig. 213. 



A pycnidium. Redrawn after Quartance and 

Shear. 



the pathologist, for they may reveal a vulnerable point of attack 
in the life history of the parasite. 

Bacteria, physiologically, are much like fungi, but their bodies 
are single-celled and not threadlike (Fig. 214). They are very 
small, — one of ordinary size is about 0.001 mm. long (^ inch) ; 
yet they multiply with such rapidity (one produces a progeny of 



490 



DISEASES OF ECONOMIC PLANTS 



16,000,000 in 6 or 8 hours under the most favorable conditions) 
that notwithstanding their minuteness they are formidable foes. 
They are, of course, invisible to the naked eye except in masses 
of countless numbers. 




Fig. 214. — Bacillus subtilis. Swarming rods with numerous fine flagella. A, after 
7J hrs.; B, after 8| hrs., with fully developed flagella. (After A. Tischer.) 



English Equivalents of Metric Units 

1 mm. 0.0394 inch, or approximately ^ inch 
1 cm. 0.3937 inch, or approximately -f inch 
1 dm. 3.9370 inches, or approximately 4 inches 
1 m. 39.37 inches, or approximately 1 yard 



\9 * is IS IT 

'IMllllllllllllllllllllllllllllllllllllllllllllfllll 



T 16 18 12 

ll l l l l llll l ll ll llll ll ll l l l l l lllll l ll l* 





F. 


C. 














-=: 






— 




202- 


:= 




192- 


— 




182- 


= 


1 




= 


~ =r ~ 




== 


— 




= 


— 




= 






__ 


— 


152 


— 





142- 



32— « -0 

Fahrenheit and Centigrade Thermometer Scales. 



INDEX 



Acanthorhynchus Vaccinii 147. 

Acervuli 17. 

Acremoniose 235. 

Acrocystis Batatae 293. 

Acrostalagmus albus 239. 

Actinonema Rosse 473. 

iEcidium elatinum 439. 

Albugo 

bliti 210, Candida 216, 241, 285, 
ipomceee-panduranae 296, Trago- 
pogonis 286. 

Alfalfa 377. 

anthracnose 381, ascochytose 
381, cercosporose, damping off 
383, dodder 385, downy mildew 
383, fusariose 380, glceospori- 
ose 383, leaf spot 377, pseudo- 
monose 382, rhizoctoniose 380, 
root rot 380, rust 383, seed mold 
383, sclerotiniose 379, stagono- 
sporose 383, Texas root rot 381, 
wilt 379, 380. 

Almond 

blight 115, cercosporose 115, 
crown gall 115, yellows 115. 

Alternaria 96, 110, 240, 383, 408. 
Brassicse 215, 230, Brassier var. 
nigrescens 217, citri 187, Dianthi 
457, panax 237, Solani 275, 
Violse 479. 

Alternariose 

cabbage 215, carnation 457, 
flax 408, ginseng 237, nastur- 
tium 469, violet 479, water- 
melon 318. 

Alternation of hosts, 11. 

Amerosporium CEconomicum 394. 

Ammoniacal copper carbonate 9, 
20, 21, 32. 



Angular leaf spot 395. 

Anthracnose 

alfalfa 381, avocado 184, bean 
198, blackberry 144, black wal- 
nut 449, blue grass 386, canta- 
loupe 219, cereals 327, chest- 
nut 438, citrus fruits 189, 
clover 389, cotton 400, cran- 
berry 148, cucumber 232, cur- 
rant 153, egg plant 237, ginseng 
239, gooseberry 160, grape 170, 
hollyhock 467, loquat 192, 
lettuce 245, mango 192, maple 
443, oat 352, orchard grass 396, 
pear 109, pepper 262, 263, 
privet 473, raspberry 175, red 
top 397, rose 476, rye 360, 
snapdragon 477, sorghum 364, 
spinach 286, squash 289, tim- 
othy 397, tomato 313, violet 
481, watermelon 318, wheat 375. 

Aposphasria 183. 

Aposphseriose 183. 

Appendix 483. 

Apple 69. 

bark canker 87, bin rot 94, 
bitter rot 69, black mold 96, 
black rot 81, black spot canker 
83, blight 80, blotch 76, blue 
mold 94, Bordeaux injury 100, 
brown rot 92, canker 81, cli- 
tocybose 98, coniothyriose 95, 
cost of spraying 47-48, crown 
gall 94, diseases — combination 
treatment 99, European canker 
87, flyspeck 95, fruit rot 91, 
hypochnose 20, 89, Illinois 
canker 86, illosporiose 88, leaf 
spot 87-88, New Hampshire 



493 



494 



INDEX 



fruit spot 96, Pacific coast 
canker 83, pink rot 91, podo- 
spheerose 94, powdery mildew 
93, ripe rot 69, root rot 98, rust 
22, 23, 78, scab 20, 74, scurf 78, 
soft rot 94, sooty blotch 94, 
sphaerthecose 93, Texas root 
rot 97, volutellose 95, wood rot 
98. wound infection 98. 

Apricot 116. 

Bacillus amylovorus 116, blight 
116, brown rot 116, phyllo- 
stictose 116, yellows 116. 

Armillaria meliea 173, 424. 

Armillariose 424. 

grape 173, plum 144. 

Artichoke 
rust 478. 

Ascochyta 

Chrysanthemi 463, Fragariae 
183, Lycopersici 237, Medicaginis 
381, Pisi 255, Primula? 472. 

Ascochytose 

alfalfa 381, chrysanthemum 463, 
egg plant 237, pea 255, primrose 
472, strawberry 183. 

Ascus 487. 

Ash 431. 

leaf spots 432, phyllostictose 
432, rust 431, white rot 21, 
431. 

Asparagus 194. 

colletotrichose 197, colletotri- 
chum 197, leopard spot 197, 
Puccinia Asparagi 194, rust 15, 
194. 

Aster 

fusariose 452, rhizoctoniose 453, 
rust 453, stem rot 452, wilt 452. 

Avocado 

anthracnose 184, Colleto- 
trichum glceosporoides 184. 

Bacillose 

calla 454, cantaloupe 218, 221, 
carrot 224, cauliflower 225, col- 



lard 229, cucumber 233, egg 
plant 236, oleander 470, potato 
277, 279, squash 289, tobacco 
300, tomato 307, watermelon 
317. 

Bacillus 253, 470. 

amylovorus 80, 116, 143, aroi- 
deae 454, carotovorus 224, melo- 
nis 221, oleracea 225, phytoph- 
thorus 279, Solanacearum 236, 
277, 300, 307, Sorghi 362, trach- 
eiphiis 218. 

Bacteria 1, 22, 245, 489. 

celery 229, discovery of 11. 

Bacterial 

disease 11, spot 459. 

Bacteriose 

beet 208, cotton 404, mulberry 
443, peach 132, plum 144, sal- 
sify 286. 

Bacterium 339. 

malvacearum 404, mori 443, 
pruni 132, teutlium 208. 

Baking soil, disinfection 54. 

Balm 453. 
rust 453. 

Bark canker 

apple 87, disease chestnut 436. 

Barley 327. 

black stem rust 330, covered 
smut 329, ergot 329, helmintho- 
sporiose 303, loose smut 327, 
powdery mildew 330, scab 330, 
yellow leaf disease 330. 

Barrel pump 41. 

Bean 198. 

anthracnose 198, bacteriosis 202, 
blight 202, cercosporose 205, 
downy mildew 204, Erysiphe 
poygoni 206, Isariopsis griseola 
206, Isariopsose 205, leaf blotch 
205, leaf spot 205, Phoma sub- 
circinata 205, Phytophthora 

' Phaseoli 204, pod blight 205, 
pod rot 204, pod spot 198, pow- 
dery mildew 206, Pseudomonas 



INDEX 



495 



Phaseoli 202, rhizoctonia 204, 
rust 201, Sclerotium Rolfsii 205, 
southern blight 205, stem rot 
204, Uromyces appendiculatus 
201. 

Bed rot 305. 

Beet 206. 

Albugo bliti 210, Bacterium 
teutlium 208, bacteriose 208, 
Cercospora beticola 206, damp- 
ing off 210, leaf spot 206, 209, 
Oospora scabies 208, Phoma 
betse 210, phomose 210, Pseudo- 
monas 209, Rhizoctonia betse 
207, rhizoctoniose 207, root 
rot 207, 210, rust 209, scab 208, 
soft rot 208, Uromyces betse 
209, white rust 210. 

Bin rot 94. 

Birch 

rust 432, sapwood rot 432. 

Bird's eye 110. 

Bitter rot 

apple 69, grape 174, pear 107. 

Blackberry 

anthracnose 144, crown gall 
144, Gloeosporium venetum 144, 
Gymnoconia interstitialis 144, 
Kuehneola albida 145, late 
rust 145, leaf spot 144, orange 
rust 144, Septoria rubi 144. 

Black knot 

cherry 118, gooseberry 160, 
hazel 440, plum 139. 

Blackleg 279. 

Black mold 

apple 96, clover 386, collard 
230, horse-radish 241, onion 254, 
255, pear 110, spinach 287. 

Black rot 

apple 81, cabbage 19, 211, 
cauliflower 225, citrus fruits 187, 
collard 229, ginseng 239, grape 
20, 161, quince 112, sweet 
potato 291, treatment 164, tur- 
nip 314. 



Black rot canker 109. 

Black rust 405. 

Black smut 355. 

Black spot 

rose 473, tomato 312. 

Black spot canker 83. 

Black stem rust 

barley 330, orchard grass 396, 
red top 396, rye 359, oat 349, 
wheat 365. 

Blast 

cranberry 146, rice 352. 

Bletia 

colletotri chose 453. 

Blight 14. 

almond 115, apple 80, apricot . 
116, bean 202, corn 339, fern 
465, ginseng 237, goldenseal 
240, lettuce 246, onion 250, 
peach 129, pear 5, 101, pine 447, 
plum 143, quince 112, sorghum 
362, tomato 307, 311, walnut 
449. 

Blossom blight 192. 

Blossom-end rot 312. 

Blotch 76. 

Blue grass 385. 

anthracnose 386, rust 385, smut 
386. 

Blue mold 

apple 94, citrus fruits 186, egg 
plant 237. 

Bluestone 10, 22. 

Bluing 445. 

Body blight 104. 

Boiled sulphur and lime 11. 

Boll rot 404. 

Bordeaux and arsenates 39. 

Bordeaux and Paris green 39. 

Bordeaux injury to apples 100. 

Bordeaux mixture 8, 9, 20, 21, 25, 
26, 106, 107. 

Botryose 

carnation 460, lily 468, orchids 
470, peony 471, primrose 473. 

Botrytis 61, 460, 468. 



496 



INDEX 



cinerea 244, longibrachiata 305, 
Peonise 471, vulgaris 470, 473. 

Bremia lactucse 245. 

Broom corn 

head smut 331, kernel smut 330. 

Broom rape 390. 

Brown rot 

apple 92, apricot 116, cherry 
119, citrus fruits 184, grape 166, 
peach 120, pear 109, plum 143, 
tobacco 304. 

Bucket pumps 41. 

Bud rot 460. 

Burgundy mixture 34. 

Burn 16. 

Butternut 432. 

glceosporiose 432. 

Cabbage 10, 211. 

alternariose 215, black rot 13, 19, 
23, 211, club root 13, 213, 
downy mildew 216, Pseudo- 
monas campestris 211, rot 23, 
sclerotiose 215, soft rot 216, 
white rust 216, wilt 216. 

Calico 306. 

Calla 

bacillose 454, cercosporose 455, 
phyllostictose 455, soft rot 454. 

Cane blight 

currant 151, raspberry 177. 

Canker 7, 16, 424. 

apple 81, fir 439, pear 104. 

Cankers 22, 23. 

Cantaloupe 217. 

anthracnose 219, bacillose 218, 
221, cercosporose 221, clado- 
sporose 224, cost of spraying 45, 
downy mildew 218, fusariose 
218, leaf blight 217, 221, phyl- 
lostictose 224, powdery mildew 
221, rot 221, southern blight 220, 
wilt 218, 223. 

Carnation 

alternariose 457, bacterial spot 
459, botryoae 460, bud rot 460, 



fusariose 458, heterosporiose 459, 
leaf mold 459, rhizoctoniose 461, 
rust 455, sporotrichose 460, 
stem rot 461, vermiculariose 457, 
volutellose 459, wilt 458. 

Carrot 

bacillose 224, soft rot 224. 

Catalpa 432. 

leaf spot 432, macrosporiose 433, 
microsphaerose 433, powdery 
mildew 433, rhizoctoniose 433, 
soft heart rot 434. 

Cauliflower 225. 

bacillose 225, black rot 225, 
pseudomonose 225, sclerotiose 
225, soft rot 225. 

Cedar 435. 

pecky cedar 436, red rot 436, 
rust 435, white rot 435. 

Celery 

bacteria 229, center blight 229, 
cercosporose 226, damping off 
229, early blight 226, late blight 
228, leaf spot 226, 228, 229, 
phyllostictose 229, rust 229, 
septoriose 228, soft rot 229. 

Center blight 229. 

Cephalothecium roseum 91. 

Ceratostomella pilifera 445. 

Cercospora 428, 468. 

althseina 467, angulata 152, 
apii 226, 255, armoracise 242, 
beticola 206, 289, Bolleana 191, 
circumcissa 133, concors 278, 
cruenta 205, 395, Cucurbitse 
221, Medicaginis 382, microsora 
440, Nicotianse 303, Persica 133, 
personata 259, Resedse 469, 
Bichardiaecola 455, rosseicola 
476, Violse 479, viticola 173. 

Cercosporose 

alfalfa 382, almond 115, bean 
205, calla 455, cantaloupe 221, 
celery 226, cucumber 233, cur- 
rant 152, gooseberry 160, grape 
173, hollyhock 467, horse-rad- 



INDEX 



497 



ish 242, linden 440, mignonette 
469, peach 133, peanut 259, 
potato 278, rose 476, spinach 
289, tobacco 303, violet 479, 
water lily 482, watermelon 318. 

Cereals 319. 

anthracnose 327, rusts 323, 
smut 319, special diseases 327. 

Cherry 116. 

black knot 118, brown rot 119, 
cost of spraying 46, curl 119, 
Cylindrosporium Padi 116, dam- 
age by leaf spot 116-117, leaf 
spot 116, mold 119, Plow- 
rightia morbosa 118, Podo- 
sphaera Oxyacanthse 119, pow- 
dery mildew 119, rust 118, 
scab 119, Schizophyllum com- 
mune 120, Sclerotinia fructigena 
119, wood rot 120, yellows 119. 

Chestnut 

anthracnose 438, bark disease 
436, leaf spot 438, monocheti- 
ose 438, septoriose 438. 

Chlorosis 16. 

Chrysanthemum 461. 

ascochytose 463, cylindrospori- 
ose 463, leaf spot 461, phyllo- 
stictose 461, powdery mildew 
463, pseudomonose 464, ray 
blight 463, rust 461, septoriose 
461, tumor 464. 

Citrus fruits 184. 

Alternaria citri 187, anthrac- 
nose 189, black rot 187, blue 
mold 186, brown rot 184, Clado- 
sporium elegans 188, Colleto- 
trichum glceosporioides 189, foot 
rot 190, Fusarium Limonis 190, 
gum disease 186, mal-di-gomma 
190, Meliola Camellia? 186, 
Penicillium digitatum 186, Peni- 
cillium italicum 186, Pythia- 
cystis citrophthora 184, scab 
188, scaly bark 185, sooty 
mold 186, wither tip 189. 

2 k 



Cladosporiose 

cantaloupe 224, pine 447. 

Cladosporium 

carpophilum 125, 142, cucu- 
merinum 234, elegans 188, ful- 
vum 310, herbarum 447, macro- 
carpum 287, viticolum 175. 

Claviceps purpurea 358. 

Cleansing sprays 20. 

Clematis 464. 
phomose 464. 

Clitocybe parasitica 98. 

Clitocybose 98. 

Clover 386. 

anthracnose 389, black mold 
386, broom rape 390, dodder 
390, leaf spot 390, macrospori- 
ose 390, rust 387, scab 390, 
sclerotiniose 386, wilt 386. 

Club root 

cabbage 213, collard 229, radish 
285, turnip 315. 

Cluster cup 18. 
gooseberry 160. 

Coleosporium Sonchi 453. 

Collard 229. 

bacillose 229, black mold 230, 
black rot 229, club root 229, 
downy mildew 229, wilt 229. 

Colletotrichose t 

asparagus 197, bletia 453, flax 
408, hollyhock 467, magnolia 
441, palm 470, pansy 470, pep- 
per 263, primrose 472, snap- 
dragon 477, squash 289. 

Colletotrichum 44, 61, 109, 197, 408, 
469, 470. 

Antirrhini 477, Bletise 453, 
carica 190, cereale 327, 352, 360, 
375, falcatum 364, glceospori- 
oides 184, 189, lagenarium 232, 
318, lindemuthianum 198, mal- 
varum 467, nigrum 263, pho- 
ooides 313, Primula? 472, Spina- 
ceae 286, Trifolii 381, 389, violae- 
tricoloris 470. 



498 



INDEX 



Combination treatment for apple 
diseases 99. 

Complementary hosts 22. 

Completoriose 466. 

Compressed air sprayers 41. 

Conidia 489. 

Coniothyriose 95. 

Coniothyrium 

diplodiella 174, Fuckelii 95, 177. 

Copper 11. 

Copper sulphate 19, 20, 27, 34. 

Coreopsis 464. 

Corn 

blight 339, ear rots 335, dry rot 
335, 338, fusariose 338, head 
smut 338, helminthosporiose 
342, pseudomonose 339, rust 
341, sclerosporose 342, smut 
331, wilt 339, yellow leaf disease 
342. 

Corrosive sublimate 19, 22, 35. 

Corticium vagum var. solani 271. 

Coryneum Beyerinkii 129. 

Cosmos 464. 

phlyctsenose 464. 

Cost of spraying 45. 
apples 48. 

Cotton 398. 

anthracnose 400, bacteriose 404, 
black rust 405, boll rot 404, 
damping off 404, frosty mildew 
403, fusariose 398, leaf blight 
403, mosaic 405, red leaf blight 
405, resistant 10, rhizoctoniose 
405, sore shin 405, shedding 406, 
Texas root rot 401, wilt 13, 23, 
398, yellow leaf disease 405. 

Cottonwood 438. 
rust 438. 

Covered smut 

barley 329, oat 349. 

Cowpea 390. 

amerosporiose 14, angular leaf 
spot 395, fusariose 390, leaf 
spot 394, powdery mildew 394, 
resistant 10, wilt 13, 390. 



Crab grass 390. 

Piriculariose 390. 

Cranberry 

Acanthorhynchus Vaccinii 147, 
anthracnose 148, blast 146, 
Exobasidium Oxycocci 148, fly- 
speck 150, gall 149, Glomerella 
rufomaculans var. Vaccinii 148, 
Guignardia Vaccinii 146, hyper- 
trophy 148, Leptothyrium pomi 

150, rot 147, scald 146, Sclero- 
tinia Oxycocci 149, sclerotiniose 

149, Synchytrium Vaccinii 149. 
Cronartium Ribicola 155. 

Crop rotation 23. 

Crown gall 

almond 115, apple 94, black- 
berry 144, peach 130, rasp- 
berry 117, rose 476, parsley 255. 

Crown rust 350. 

Cryptosporella anomala 440. 

Cucumber 

Acremoniose 235, anthracnose 

232, bacillose 233, cercosporose 

233, cost of spraying 45, damp- 
ing off 234, downy mildew 231, 
fruit spot 234, fusariose 233, 
leaf blight 234, phyllostictose 
233, powdery mildew 234, scle- 
rotiniose 233, timber rot 233, 
wilt 233. 

Cucurb spraying 235. 
Curl 

cherry 119, peach 20, 126. 
Currant 

anthracnose 153, cane blight 

151, Cercospora angulata 152, 
cercosporose 152, Cronartium 
Ribicola 155, dematophorose 
155, European rust 155, knot 

150, leaf spot 152, Pleonectria 
Berolinensis 150, powdery mil- 
dew 155, Pseudopeziza Ribis 
153, Puccinia Ribis 155, root 
rot 155, rust 155, septoriose 152, 
sphaerothecose 155. 



INDEX 



499 



Cuscuta 385. 
Cyclamen 464. 

glomerellose 465, phomose 464. 
Cycloconium oleaginum 193. 
Cylindrosporiose 

Chrysanthemum 463, hop 241, 

tomato 311. 
Cylindrosporium 311. 

Chrysanthemi 463, Humuli 241, 

padi 116, 141, pomi 96. 

Dahlia 

phomose 465, powdery mildew 

465. 
Damage caused by plant diseases 12. 
Damping off 60. 

alfalfa 383, beet 210, celery 229, 

cotton 404, cucumber 234, egg 

plant 236, ginseng 240, lettuce 

244, nasturtium 469, onion 255, 

pea 259, pine 446, radish 285, 

rice 356, tobacco 305, tomato 

313. 
Dasyscypha resinaria 439. 
Decay in live trees 409. 
Decay of dead parts 427. 
Decay of dead trees 427. 
Dematophora 160. 

necatrix 172, 191, 427. 
Dematophorose 427. 

currant 155, grape 172. 
Dewberry 

double blossom 155, cane blight. 

157, leaf blight 157. 
Diaporthe parasitica 436. 
Die back 

peach 129, plum 144. 
Diplodia 

macrospora 335, zese 335. 
Direct firing 58. 
Disease 

bacterial 11, symptoms 14. 
Diseased localities 23. 
Diseases 

number of 5, of special crops 69, 

physiological 1. 



Disinfection 

formalin 58, soil 54. 

Dodder 

alfalfa 385, clover 390. 

Dormant sprays 20. 

Dothidella ulmea 438. 

Dothidellose 438. 

Double blossom 155. 

Downy mildew 

alfalfa 383, bean 204, cabbage 
215, cantaloupe 218, collard 
229, cucumber 231, grape 7, 166, 
lettuce 245, onion 250, pansy 
471, potato 263, pumpkin 285, 
rose 476, spinach 288, squash 
210, tomato 311, turnip 315, 
violet 481, watermelon 318. 

Dracaena 465. 

Drop 

lettuce 242, parsley 255. 

Drupaceous fruits 115. 

Dry rot 429. 

corn 335, 338, 429, sweet potato 
294. 

Dusting machines 44. 

Ear rots 335. 

Early blight 

celery 226, potato 275. 

Egg plant 

anthracnose 237, ascochytose 
237, bacillose 236, blue mold 
237, damping off 236, glce- 
osporiose 237, leaf spot 236, 
237, nectriose 236, phyllostic- 
tose 236, wilt 236. 

Elm 438. 

dothidellose 438, leaf spot 438, 
phyllostictose 439, powdery mil- 
dew 439, uncinulose 439. 

End rot 240. 

English equivalents of the metric 
units 490. 

Entyloma Ellisii 287. 

Ergot 

barley 329, rye 358. 



500 



INDEX 



Erysiphe 

cichoracearum 289, 463, 466, 
478, communis 465, graminis 
375, polygoni 206, 221, 234, 
258, 315, 394. 

European canker 

apple 87, quince 115. 

European rust 155. 

Excision 21. 

Exoascus 

deformans 126, pruni 141. 

Exobasidium Oxycocci 148. 

Fabrsea maculata 108, 112. 

Factory-boiled lime-sulphur 36. 

Ferns 

blight 465, completoriose 466, 
phyllostictose 465. 

Fiber plants 398. 

Fiber rot 240. 

Field sprayers 42. 

Fig 190. 

Cercospora Bolleana 191, Col- 
letotrichum carica 190, Dema- 
tophora necatrix 191, fruit rot 

190, Fusariurh roseum 191, leaf 
blight 191, root rot 191, rust 

191, Uredo Fici 191, yellow 
rust 191. 

> ilbert 439. 

Fir 439. 

canker 439, rust 439. 

Fire blight 101. 

"Flax 

alternariose 408, colletotrichum 
408, fusariose 406, rust 408, wilt 
406. 

Flower blight 104. 

Flowers of sulphur 20, 35. 

Flyspeck 

apple 95, cranberry 150. 

Fomes 

annosus 425, applanatus 425, 
Everhartii 420, fomentarius 421, 
fulvus 419, igniarius 414, nigri- 
cans 418, Ribis 448, rimosus 441 . 



Foot rot 190. 

Forage crops 377. 

Formaldehyde 35. 

Formalin 10, 12, 19, 35. 

disinfection 58, treatment fov 
smut 346. 

Frenching 306. 

Frosty milder 

cotton 403, peach 133. 

Fruit rot 

apple 91, fig 190. 

Fruit rots 23. 

Fruit spot 234. 

Fumago vagans 313. 

Fumagose 313. 

Fungi 1, 486. 

Fungicides 25. 

Fusariose 

alfalfa 380, aster 452, cabbage 
216, cantaloupe 218, carnation 
458, corn 338, cotton 398, 
cowpea 390, cucumber 233, flax 
406, ginseng 238, pansy 471, 
pine 446, potato 275, tomato 
308, watermelon 315. 

Fusarium 216, 308, 338, 380, 446, 
452, 458. 

Limonis 190, lini 406, oxy- 
sporum 275, roseum 191, Rubi 
155, vasinfectum 238, 390, 398, 
vasinfectum var. niveum 218, 
315, Vioke 471. 

Fusicladiose 444. 

Fusicladium dendriticum var. erio- 
botrya3 192, effusum 444. 

Fusicoccum viticolum 171. 

Gall 

cranberry 149, oleander 470. 

General diseases 60, 409. 

Gibberella 330. 

saubinetii 376, 390. 

Ginseng 237. 

acrostalagmose 239, alternariose 
237, black rot 237, blight 237, 
damping off 240, end rot 240, 



INDEX 



501 



fiber rot 240, fusariose 238, 
leaf anthracnose 240, pestallo- 
ziose 240, soft rot 240, stem 
anthracnose 239, wilt 239. 
Gloeosporiose 

alfalfa 383, butternut 432, egg 
plant 237, maple 443, privet 
473, rose 476, spurge 478, 
violet 481. 
Glceosporium 61. 

apocryptum 443, caulivorum 
389, cingulatum 473, euphor- 
bia? 478, Juglandis 432, Medi- 
caginis 383, melongense 237, 
nervisequum 448, piperatum 
262, Rosae 476, venetum 144, 
175, Viol® 481. 
Glomerella 

Gossypii 400, rufomaculans 69, 
107, 115, 174, rufomaculans 
var. cyclaminis 465, psidii 191. 
Glomerellose 

Cyclamen 465. 
Gnomonia 

Juglandis 449, veneta 448. 
Gnomoniose 

black walnut 449, sycamore 448. 
Golden glow 

powdery mildew 466. 
Goldenseal 240. 

blight 240. 
Gooseberry 

anthracnose 160, black knot 
160, cluster-cup 160, dema- 
tophora 160, leaf spot 160, 
powdery mildew 19, 157, Puc- 
cinia Grossulari® 160, root rot 
160, septoriose 160, Sph®ro- 
theca mors-uv® 157. 
Granville wilt 300. 
Grape 52. 

anthracnose 170, Armillaria mel- 
lea 173, armillariose 173, bird's 
eye 170, bitter rot 174, black 
rot 20, 161, black rot treat- 
ment 164, brown rot 166, Cer- 



cospora viticola 173, cercospo- 
rose 173, Cladosporium viti- 
colum 175, Coniothyrium dip- 
lodiella 174, cost of spraying 46, 
Dematophora necatrix 172, de- 
matophorose 172, disease 14, 
downy mildew 7, 166, Fusi- 
coccum viticolum 171, Glome- 
rella rufomaculans 174, gray 
rot 166, Guignardia Bidwellii 
161 Melanconium fuligineum 
174, melanconiose 174, mildew 
8, necrosis 171, Pestalozzia 
uvicola 175, pestalloziose 175, 
Plasmopara viticola 1 66, powdery 
mildew 19, 164, resistant 10, 
ripe rot 174, root rot 172, 173, 
scab 175, Septosporium hetero- 
sporium 175, septosporiose 175, 
Sphaceloma ampelinum 170, 
Uncinula necator 164, uncinu- 
lose 164, white rot 174. 

Gray mold 244. 

Gray rot 166. 

Green smut 354. 

Guava 191. 

Glomerella psidii 1 9 1 , ripe rot 191. 

Guinardia 

Bidwellii 161, Vaccinii 146. 

Gum disease 186. 

Gymnoconia interstitialis 144. 

Gymnoconiose 144. 

Gymnosporangium 435. 

clavipes 110, globosum 106, 
macropus 78. 

Hazel 440. 

black knot 440. 
Head smut 

broom corn 331, corn 335, 

sorghum 364. 
Heart rot 23, 414, 418, 419, 420, 

locust 441, sassafras 448. 
Hedera 468. 
Helminthosporiose 

barley 330, corn 342. 



502 



INDEX 



Helminthosporium 

carpophilum 134, gramineum 
330, inconspicuum 342, ineon- 
spicuum var. Brittanicum 352, 
sativum 330. 

Heterosporiose 

carnation 459, spinach 288. 

Heterosporium 

echinulatum 459, variable 288. 

Hibiscus Sabariffa 286. 

Historical 3. 

Hollyhock 

anthracnose 467, cercosporose 
467, colletotrichose 467, phyllo- 
stictose 467, rust 466. 

Home-boiled lime-sulphur 36. 

Hop 240. 

cylindrosporiose 241, powdery 
mildew 240. 

Horse-chestnut 440. 

leaf spot 440, phyllostictose 440. 

Horse-radish 241. 

black mold 241, cercosporose 
242, leaf spot 242, leaf blight 
241, ramulariose 241, septoriose 
241, white rust 241. 

Hosts, alternation of 11. 

Hot-water treatment 10, 12, 372. 

Hydnum erinaceus 418. 

Hydrangea 

cercosporose 468, phyllostictose 
46S. 

Hydrastis 240. 

Hypertrophy 148. 

Hyphae 17. 

Hypochnose 

apple 20, S9, pear 109, quince 
115. 

Hypochnus 91. 
ochroleuca 89. 

Hypoderma Desmazieri 445. 

Hypodermose 445. 

Illinois canker 86. 
Illosporiose 8S. 
Illosporium malifoliorurn 88. 



Insects 1. 

Inverted pan method 55. 

Isariopsis griseola 205. 

Isariopsose 205. 

Ivy 468. 

Japan clover 395. 

powdery mildew 395. 

Kernel smut 

broom corn 330, sorghum 362. 
Kinds of smut 319. 
Knapsack sprayer 41. 
Knot 

currant 150, oleander 470, 

olive 192. 
Kuehneola albida 145. 

Lasiodiplodia tubericola 294. 

Lasiodiplodiose 294. 

Late blight 

celery 228, potato 263. 

Late rust 145. 

Leaf anthracnose 240. 

Leaf blight 

cantaloupe 217, 221, cotton 403, 
cucumber 234, fig 191, horse- 
radish 241, pear 108, pine 445, 
poplar 447, quince 112, spinach 
2S9, strawberry 183, sweet 
potato 295. 

Leaf blotch 

bean 205, potato 278. 

Leaf curl 444. 

Leaf mold 

carnation 459, tomato 310. 

Leaf perforation 245. 

Leaf spot 141. 

alfalfa 377, apple 87, 88, ash 
432, bean 205, beet 206, 209, 
blackberry 144, catalpa 432, 
celery 226. 22S. 229. cherry 116. 
chestnut 438, chrysanthemum 
461, clover 390, cowpea 394, 
currant 152, egg plant 236, 237, 
elm 438, gooseberry 160, horse- 



INDEX 



503 



chestnut 440, horse-radish 242, 
linden 440, locust 441, maple 
442, 443, parsnip 255, pea 259, 
peanut 259, pear 108, pepper 
263, raspberry 177, rose 476, 
strawberry 181, sweet potato 
295, tomato 311, violet 479, 481. 

Leopard spot 197. 

Leptosphseria tritici 376. 

Leptosphaerose 376. 

Leptostromella hypophylla 441. 

Leptothyrium pomi 95, 150. 

Lettuce 13, 242. 

anthracnose 245, blight 246, 
damping off 244, downy mil- 
dew 245, drop 13, 242, gray 
mold 244, leaf perforation 245, 
rosette 244, sclerotiniose 242, 
septoriose 246, soft rot 245, 
wilt 242. 

Light 1. 

Lilac 468. 

Lily 468. 

Lime-sulphur 11, 36. 

Lime-sulphur mixtures 20. 

Linden 440. 

cercosporose 440, leaf spot 440. 

Little peach 139. 

Little potato 271. 

Liver of sulphur 20. 

Locust 441. 

heart rot 441, leaf spot 441. 

Loose smut 

barley 327, oat 343, wheat 370. 

Lophodermium brachysporum 445. 

Loquat 

anthracnose 192, blossom blight 
192, Fusicladium dendriticum 
var. Eriobotryae 192, scab 192. 

Machinery 10, 11. 

Macrophoma curvispora 83. 

Macrosporiose 

catalpa 433, clover 390, horse- 
radish 241, pepper 263, turnip 
315. 



Macrosporium 

catalpse 433, herculeum 241, 
315, longipes 304, parasiticum 
254, Porri 255, sarciniseforme 
390, Solani 312, tabacinum 
304. 

Magnolia 441. 

colletotrichose 441. 

Mal-di-gomma 190. 

Mango 192. 

anthracnose 192. 

Maple 442. 

anthracnose 443, glceosporiose 
443, leaf spot 442, 443, phyllo- 
stictose 442, powdery mildews 
443, rhytismose 443, tar spot 
443. 

Marsonia 

Juglandis 449, ochroleuca 438, 
perforans 245, Populi 447, Vio- 
la- 481. 

Marsoniose 

poplar 447, violet 481. 

Melampsora 438. 

Betulina 432, Lini 408, Popu- 
lina 447, saliciscapras 450. 

Melanconiose 174. 

Melanconium fuligineum 174. 

Melon wilt 13, 22, 23. 

Meruliose 429. 

Merulius lacrymans 429. 

Microsphserose 

catalpa 433, oak 444, pecan 445. 

Mignonette cercosporose 469. 

Mildew 7, 11, 16. 

Millet 342. 

piriculariose 342, smut 343. 

Mirosphaera 444. 

alni 445, 468, diffusa 395, 
elevata 433, Euphorbias 286. 

Mistletoe 431. 

Mold 

cherry 119, peach 120. 

Monilochsetes infuscans 295. 

Monochetia pacyospora 438. 

Monochetiose 438. 



504 



INDEX 



Mosaic 

cotton 405, tobacco 306, tomato 

314. 
Mulberry 443. 

bacteriose 443. 
Mushrooms 246. 

mycogonose 246. 
Muskmelon 217, 247. 
Mycelium 486. 
Mycogone perniciosa 246. 
Mycogonose 246. 
Mycosphaerella 

citrullina 223, gossypina 403. 
Mycosphaerellose 317. 
Myxosporium corticolum 87. 

Nasturtium 

alternariose 469, damping off 
469, pseudomonose 469. 

Necrosis 171. 

Nectria 

cinnabarina 87, 115, 424, ditis- 
sima 87, 115, Ipomcese 236. 

Nectriose 

egg plant 236, sweet potato 294. 

Nematode galls 67. 

New Hampshire fruit spot 96. 

Nozzles 44. 

Numularia 424. 
discreta 86. 

Nutriment 1. 

Oak 444. 

leaf curl 444, microsphserose 
444, powdery mildew 444, taph- 
rinose 444. 

Oat 343. 

anthracnose 352, black stem 
rust 349, covered smut 349, 
crown rust 350, loose smut 343, 
powdery mildew 352, phyllo- 
stictose 350, pseudomonose 351, 
scab 350, smut 14, 19, ustilagose 
349, yellow leaf disease 352. 

(Edema 313. 

Oidium Chrysanthemi 463. 



Oleander 

bacillose 470, gall 470, knot 
470. 

Olive 192. 

Cycloconium oleaginum 193, 
knot 192, peacock leaf spot 193, 
Pseudomonas Savastanoi 192, 
sooty mold 193. 

Onion 

black mold 254, 255, blight 250, 
damping off 255, downy mil- 
dew 250, smut 13, 247, soft rot 
253, vermiculariose 252. 

Oospora scabies 208, 267. 

Orange rust 144. 

Orange leaf rust 

rye 359, wheat 367. 

Orchard grass 

anthracnose 396, black stem 
rust 396, rust 396, scoleco- 
trichose 396. 

Orchids 470. 

Ornamental plants 451. 

Orobanche 

minor 390, tobacco 307. 

Osage orange 444. 
rust 444. 

Ozoniose 62, 427. 

Ozonium omnivorum 380, 401, 427. 

Pacific coast canker 83. 

Pale rot 115. 

Palm 470. 

Pan firing 58. 

Pansy 

colletotrichose 470, downy mil- 
dew 471, fusariose 471, rust 471. 

Parsley 255. 

drop 255, crown rot 255, sclero- 
tiniose 255. 

Parsnip 255. 
leaf spot 255. 

Pea 255. 

ascochytose 255, damping off 
259, leaf spot 259, Pleospora 
259, powdery mildew 258, rhi- 



INDEX 



505 



zoctoniose 259, rust 259, septo- 
riose 259, spot 255. 
Peach 120. 

Bacterium pruni 132, bacteri- 
ose 132, blight 129, brown rot 
120, brown rot control 124, 
Cercospora circumcissa 133, 
Cercosporella persica 133, cer- 
cosporose 133, Cladosporium 
carpophilum 125, Coryneum 
Beyerinkii 129, crown gall 130, 
curl 20, 126, curl damage 126, 
curl prevention 127, dieback 
129, Exoascus deformans 126, 
frosty mildew 133, gain from 
spraying 128, Helminthospo- 
rium carpophilum 134, leaf 
curl 14, little peach 139, mold 
120, mummy 122, Phoma Per- 
sicae 134, phomose 134, Phyl- 
losticta circumcissa 133, phyl- 
lostictose 133, Podosphaera Ox- 
ycanthae 13.2, podosphaerose 

132, powdery mildew 132, 133, 
Pseudomonas tumefacines 130, 
Puccihia Pruni-spinosae 134, 
pustular spot 134, rosette 137, 
rot 22, rust 134, scab 125, Sclero- 
tinia fructigena 120, shot hole 
129, 133, Sphaerotheca pannosa 

133, sphaerothecose 133, stem 
blight 134, Texas root rot 133, 
Valsa leucostoma 129, yellows 
135. 

Peaches 

mildew 7. 

Peacock leaf spot 193. 

Peanut 

cercosporose 259, leaf spot 259. 

Pear 

active blight 103, Alternaria 110, 
anthracnose 109, Bacillus amy- 
lovorus 101, bitter rot 107, 
black mold 110, black rot can- 
ker 109, blight 5, 22, 104, blight 
damage 101, body blight 104, 



brown rot 109, canker 104, col- 
letotrichum 109, cost of spray- 
ing 46, Fabraea maculata 108, 
fire blight 101, flower blight 
104, Glomerella rufomaculans 
107, Gymnosporangium glo- 
bosum 106, hypochnose 109, 
leaf blight 108, leaf spot 108, 
podosphaerose 107, powdery mil- 
dew 107, resistant to blight 104, 
ripe rot 107, rust 106, scab 52, 
107, Septoria piricola 108, Sphae- 
ropsis malorum 109, sphaerothe- 
cose 107, susceptible to blight 
104, Texas root rot 110, Thele- 
phora pedicellata 109, thele- 
phorose 109. 

Pecan 444. 

fusicladiose 444, microsphaerose 
445, scab 444. 

Pecky cedar 436. 

Penicilliose 295. 

Penicillium 295. 

digitatum 186, italicum 186, 
glaucum 94. 

Peony 471. 

Pepper 257. 

anthracnose 262, 263, colletro- 
trichose 263, leaf spot 263, 
macrosporiose 263, phyllostic- 
tose 263, southern blight 259, 
wilt 259. 

Perfection of produce 50. 

Peridermiose 446. 

Peridermium 

acicolum 446, cerebrum 446. 

Perithecia 17, 487. 

Permanent steam disinfectors 54. 

Peronospora 

Cubensis 218, effusa 288, para- 
sitica 215, schleideni 250, sparsa 
476, Trifoliorum 383, Violas 481. 

Pestalozzia 

funerea 240, uvicola 175. 

Pestalozziose 

ginseng 240, grape 175. 



506 



INDEX 



Phlyctaena sp. 464. 

Phlyctsenose 464. 

Phoma 61, 464, 477. 

Batata 294, Betse 210, Cycla- 
menae 464, Cydonse 115, Dah- 
lia? 465, Persicse 134, Solani 236, 
subcircinata 205. 

Phomose 

beet 210, clematis 464, cycla- 
men 464, dahlia 465, peach 134, 
snapdragon 477. 

Phoradendron 431. 

Phragmidium 

speciosum 476, subcorticum 475. 

Phyllachora 

pomigena 94, Trifolii 386. 

Phyllactinose 439. 

Phyllosticta 263, 350, 461. 

acericola 442, althseina 467, 
ampelopsidis 481, Apii 229, 
bataticola 295, Catalpse 432, 
Chenopodii 289, circumcissa 133, 
cucurbitacearum 224, hortorum 
236, Hydrangea? 468, maculicola 
465, primulicola 472, prunicola 
78, Pteridis 465, Richardise 455, 
solitaria 76, sphseropsidea 440, 
Viola? 481, viridis 432. 

Phyllostictose 

apricot 116, ash 432, calla 455, 
cantaloupe 224, celery 229, 
chrysanthemum 461, cucumber 
233, Dracaena 465, egg plant 
236, ferns 465, hollyhock 467, 
horse-chestnut 440, hydrangea 
468, maple 442, oat 350, peach 
133, pepper 263, primrose 472, 
spinach 289, sweet potato 295, 
violet 481, Virginia creeper 481. 

Phylloxera 

grapes resistant to 10. 

Physiological 483. 
diseases 1. 

Physopella 444. 

Phytophthora 61. 

infestans 263, 311, Phaseoli 204. 



Pine 445. 

blight 447, bluing 445, clado- 
sporiose 447, damping off 446, 
fusariose 446, hypodermose 445, 
leaf blight 445, peridermiose 
446, red rot 447, rust 446, twig 
blight 445. 

Pink 472. 

Pink rot 91. 

Pip 357. 

Piped rot 418. 

Piricularia 

grisea 342, oryzae 352, 390. 

Piriculariose 

crab grass 390, millet 342. 

Plant disease 1. 

ancient recognition 11, damage 
caused by 12, prevention 18. 

Plant pathology 1, 11. 

Plasmodiophora Brassicse 213. 

Plasmopara viticola 166. 

Pleonectria Beriolinensis 150. 

Pleospora 

pea 259, Pisi 259, Tropceoli 469. 

Plowrightia morbosa 118, 139. 

Plum 

armillariose 144, Bacillus amy- 
lovorus 143, bacteriose 144, 
black knot 139, blight 143, 
brown rot 143, brown rot dam- 
age 143, Cladosporium carpo- 
philum 142, cost of spraying 46, 
Cylindrosporium padi 141, die 
back 144, Exoascus pruni 141, 
leaf spot 141, leaf spot damage 

142, Plowrightia morbosa 139, 
pockets 141, podosphaerose 

143, powdery mildew 143, Puc- 
cinia pruni-spinosse 143, root 
rot 144, rust 143, scab 142, 
Sclerotinia fructigena 143, spray- 
ing 52, valsose 144, yellows 
143. 

Pod blight 205. 
Pod rot 204. 
Pod spot 198. 



INDEX 



507 



Podosphaera 

leucotrichia 94, Oxyacanthse 
119, 132. 

Podosphaerose 

apple 94, peach 132, pear 107, 
plum 143. 

Point rot 312. 

Pole burn 305. 

Pole rot 305. 

Polyporose 425, 429. 

Polyporus 

betulinus 432, carneus 436, 
fraxinophilus 431, juniperinus 
435, obtusus 419, pergamenus 
429, pinicola 429, 422, pondero- 
sus 447, Schweinitzii 426, squa- 
mosum 421, subacidus 419, sul- 
phureus 416, versicolor 425. 

Polysticta versicolor 429, 434. 

Pomaceous fruits 69. 

Poplar 447. 

leaf blight 447, marsoniose 447, 
powdery mildew 447, rust 447, 
uncinulose 447. 

Potassium sulphide 34. 

Potato 10, 13, 263. 

bacillose 277, 279, black leg 279, 
blight 13, 14, 23, cercosporose 
278, cost of spraying 46, downy 
mildew 236, early blight 275, 
fusariose 275, late blight 14, 263, 
leaf blotch 278, little potato 271, 
rosette 271, rot 279, scab 23, 
267, spraying 281, stem rot 271, 
tip burn 279, wilt 275, 277. 

Powdery mildew 20. 

apple 93, barley 330, bean 206, 
cabbage 216, cantaloupe 221, 
catalpa 433, cherry 119, chrys- 
anthemum 463, cowpea 394, cu- 
cumber 234, currant 155, dahlia 
465, elm 439, golden glow 466, 
gooseberry 19, 157, grape 19, 
164, hop 240, Japan clover 395, 
lilac 468, maple 443, oak 444, 
oat 352, pea 258, peach 132, 



133, pear 107, plum 143, poplar 
447, pumpkin 285, rose 19, 475, 
roselle 286, rye 362, strawberry 
183, squash 289, sycamore 449, 
turnip 315, verbena 478, Vir- 
ginia creeper 482, wheat 375, 
willow 451. 

Power sprayer 44. 

Prepared Bordeaux 32. 

Prevention of plant diseases 18. 
methods 19, historical 5. 

Preventive treatment for smut 322. 

Primrose 

ascochytose 472, botryose 473, 
colletotrichose 472, phyllostic- 
tose 472, ramulariose 472. 

Privet 

anthracnose 473, glceosporiose 
473. 

Profits from spraying 50. 

Protective sprays 20. 

Protocoronospora nigricans 397. 

Pseudomonas 209, 469. 

Avense 351, campestris 211, 225, 
314, Juglandis 449, Medicagi- 
nis 382, Phaseoli 202, Sava- 
stanoi 192, Stewarti 339, tume- 
faciens 130, 131, 177, 464. 

Pseudomonose 

alfalfa 382, cauliflower 225, 
corn 339, chrysanthemum 464, 
nasturtium 469, oat 351, walnut 
449. 

Pseudoperonospora cubensis 231. 

Pseudopeziza 

Medicaginis 377, Ribis 153, Tri- 
folii 390. 

Public plant sanitation 24. 

Puccinia 

arenarise 472, Asparagi 194, 
bullata 229, Chrysanthemi 461, 
Fraxini 431, graminis 330, 349, 
359, 396, 397, Grossulariee 160, 
Helianthi 478, malvacearum 
466, Menthse 453, Poarum 385, 
Pruni-spinosae 143, Rhamni 396, 



508 



INDEX 



350, Ribis 155, rubego-vera 359, 
Sorghi 341, Tragopogonis 286, 
triticina 367, Violas 471. 

Pumpkin 285. 

downy mildew 285, powdery 
mildew 285. 

Pustular spot 134. 

Pycnidia 17, 489. 

Pythiacystis citrophthora 184. 

Pythium 61. 

De Baryanum 236. 

Quack grass 

smut 396, urocystose 396. 

Quince 

Bacillus amylovorus 112, black 
rot 112, blight 112, European 
canker 115, Fabrsea maculata 
112, fruit spot 112, Glomerella 
rufomaculans 115, Gymnospo- 
rangium clavipes 110, hypoch- 
nose 115, knot 111, leaf blight 
112, Nectria cinnabarina 115, 
Nectria ditissima 115, pale rot 
115, Phoma Cydonise 115, ripe 
rot 115, rust 110, Sphaeropsis 
malorum 112. 

Radish 285. 

club root 285, damping off 285, 
white rust 285. 

Ramularia 

areola 403, Armoracise 241, 
Primulse 472. 

Ramulariose 

horse-radish 241, primrose 472. 

Raspberry 

anthracnose 175, cane blight 
177, Coniothyrium Fuckelii 177, 
crown gall 177, Glceosporium 
venetum 175, gymnoconiose 177, 
leaf spot 177, rust 177, Pseudo- 
monas tumefaciens 177, septo- 
riose 177, Sphaerella rubina 180, 
sphaerellose 180, yellows 180. 

Ray blight 463. 



Red heart rot 416. 

Red leaf blight 405. 

Red rot 425. 

cedar 436, pine 447. 

Red top 

anthracnose 397, black stem 
rust 396, smut 397. 

Resistant 

pears 104, varieties 23. 

Rhizoctonia 61, 204, 240, 244, 305, 
314, 405, 461, 464. 
Beta? 207, Medicaginis 380. 

Rhizoctoniose 61. 

alfalfa 380, aster 453, beet 207, 
carnation 461, catalpa 433, cot- 
ton 405, pea 259, tobacco 305, 
violet 481. 

Rhizopus nigricans 279, 289. 

Rhododendron 

Synchytrium Vaccinii 150. 

Rhytisma 

acerinum 443, punctatum 443. 

Rhytismose 
maple 443. 

Rice 352. . 

black smut 355, blast 352, 
damping off 356, green smut 354, 
pip 357, rotten neck 352, rust 357, 
speck 357, spotted blight 357. 

Ripe rot 

apple 69, grape 174, guava 191, 
pear 107, quince 115. 

Root knot 67. 

Root rot 426, 427. 

alfalfa 380, apple 98, beet 207, 
210, currant 155, gooseberry 
160, grape 172, 173, plum 144, 
tobacco 296. 

Root rots 424. 

Rose 

anthracnose 476, black spot 473, 
cercosporose 476, crown gall 
476, downy mildew 476, glce- 
osporium 476, leaf spot 476, 
powdery mildew 19, rust 475, 
476, sphserellose 476, 



INDEX 



509 



Roselle 286. 

powdery mildew 286. 

Rosette 

lettuce 244, peach 137, potato 
271, tomato 314. 

Rot 14, 419, 422. 

cantaloupe 221, cranberry 147, 
potato 279. 

Rotten neck 352. 

Rust 16. 

alfalfa 383, apple 78, artichoke 
478, ash 431, asparagus 194, 
aster 453, balm 453, bean 201, 
beet 209, birch 432, blue grass 
385, carnation 455, cedar 435, 
celery 229, cereal 323, cherry 
118, chrysanthemum 461, clover 
387, corn 341, cotton 438, cur- 
rant 155, fig 191, fir 439, flax 
408, hollyhock 466, orchard 
grass 396, osage orange 444, 
pansy 471, pea 259, peach 134, 
pear 106, pine 446, pink 472, 
plum 143, poplar 447, quince 
110, raspberry 177, rice 357, 
rose 475, 476, salsify 286, sun- 
flower 478, teosinte 365, tim- 
othy 397, tomato 312, willow 
450. 

Rye 358. 

anthracnose 360, black stem 
rust 359, ergot 358, orange leaf 
rust 359, powdery mildew 362, 
scab 362, smut 360. 

Salsify 286. 

bacteriose 286, rust 286, white 
rust 286. 

Sap rot 23, 429. 

Sapwood rot 421, 432. 

Sar smut treatment 347. 

Sassafras 448. 

Scab 15. 

apple 20, 74, barley 330, beet 
208, cherry 119, citrus fruits 
188, clover 390, grape 175, lo- 



quat 192, oat 350, peach 125, 
pecan 444, plum 142, potato 
267, rye 362, turnip 315, wheat 
376. 

Scald 146. 

Scaly bark 185. 

Schizophyllum commune 98, 120. 

Sclerospora macrospora 342. 

Sclerosporose 342. 

Sclerotia 18, 487. 

Sclerotinia 61, 305. 

fructigena 92, 119, 120, 143, 
Libertiana 215, 233, 242, 255, 
Oxycocci 149, Trifoliorum 379, 
386. 

Sclerotiniose 

alfalfa 379, cabbage 215, cauli- 
flower 225, clover 386, cran- 
berry 149, cucumber 233, let- 
tuce 242, parsley 255, tobacco 
305. 

Sclerotiose 62. 

Sclerotium 239. 

Rolfsii 62, 205, 220, 259, 313. 

Scolecotrichose 396. 

Scolecotrichum graminis 396. 

Scurf 

apple 78, sweet potato 294. 

Sedum 

septoriose 477, vermiculariose 
477. 

Seed mold 383. 

Self-boiled lime-sulphur 37. 

Septoria 376. 

Armoracese 241, Chrysanthemi 
461, consimilis 246, Lactucse 246, 
Lycopersici 311, ochroleuca 438, 
Petroselina var. Apii 226, piri- 
cola 108, Pisi 259, Ribis 152, 
Rubi 144, Sedi 477. 

Septoriose 

celery 228, chestnut 438, chrys- 
anthemum 461, currant 152, 
gooseberry 160, horse-radish 
241, lettuce 246, raspberry 177, 
pea 259, Sedum 477, wheat 376. 



510 



INDEX 



Septosporiose 175. 

Septosporium heterosporium 175. 

Shot hole peach 129, 133. 

Slime molds 1. 

Small fruits 144. 

Smut 16. 

bluegrass 386, cereal 319, corn 
331, formalin treatment 346, 
hot-water treatment 12, 372, 
kinds 319, millet 343, oat 19, 
onion 247, quack grass 396, 
red top 397, rye 360, Sar treat- 
ment 347, tall oat grass 397, 
teosinte 365, timothy 397, 
wheat 19. 

Snapdragon 

anthracnose 477, colletotrichose 
477, phomose 477. 

Soda Bordeaux 30, 31. 

Soft rot 419. 

apple 94, beet 208, cabbage 216, 
calla 454, carrot 224, catalpa 
434, cauliflower 225, celery 229, 
ginseng 240, lettuce 245, onion 
253, sweet potato 289. 

Soil 1. 

Soil diseases 63. 

Soil disinfection 54. 

Sargent method 57, surface 
firing 57. 

Soil rot 293. 

Sooty blotch 94. 

Sooty mold 

citrus fruits 186, olive 193. 

Sore shin 405. 

Sorghum 

anthracnose 364, blight 362, 
head smut 364, kernel smut 
362. 

Sori 17. 

Southern blight 

bean 205, cantaloupe 220, pep- 
per 259, tomato 313. 

Special diseases 327. 

Special hosts 431. 

Speck 357. 



Sphaceloma ampelinum 170. 

Sphacelotheca 

Reiliana 364, Sorghi 362, 330. 

Sphaerella 

Fragarise 181, rosigera 476, ru- 
bina 180. 

Sphserellose 

rose 476, strawberry 180. 

Sphseronema fimbriatum 291. 

Spharopsis malorum 81, 109, 112. 

Sphaerotheca 

Humuli 183, 240, mali 93, mors- 
uvae 157, pannosa 475. 

Sphserothecose 

apple 93, currant 155, peach 
133, pear 107, strawberry 183. 

Spinach 286. 

anthracnose 286, black mold 
287, cercosporose 289, downy 
mildew 288, heterosporiose 288, 
leaf blight 289, phyllostictose 
289, white smut 287. 

Sporotrichose 460. 

Sporotrichum anthophilum 460. 

Spot 15, 17. 

pea 255, vetch 397, violet 
479. 

Spotted blight 357. 

Spray 

cleansing 20, dormant 20, pro- 
tective 20. 

Spraying 

at Avon, Va. 49, cost of 45, 
cucumbers 45, cucurb 235, 
machinery 39, potatoes 46, 281, 
profits from 50. 

Spurge 

glceosporiose 478. 

Squash 289. 

anthracnose 289, bacillose 289, 
colletotrichose 289, downy mil- 
dew 289, powdery mildew 289, 
wilt 289. 

Stagonospora carpathica 383. 

Stagonosporose 383. 
alfalfa 383. 



INDEX 



511 



Stem blight 134. 

Stem rot 

aster 452, bean 204, carnation 
461, potato 271, sweet potato 
294, tobacco 305. 

Stinking smut 368. 

Stock solutions 27. 

Strawberry 181. 

Ascochyta Fragarise 183, as- 
cochytose 183, Aposphseria 183, 
aposphseriose 183, leaf blight 
183, leaf spot 181, 183, powdery 
mildew 183, Sphaerella Fraga- 
rise 181, Sphaerotheca Humuli 
183, sphaerothecose 183. 

Sulphur 7, 11. 

flowers of 20, liver of 20. 

Sulphur and lime boiled 11. 

Sulphur-soda soap 35. 

Sulphuring and dusting machinery 
44. 

Sunflower 478. 

Surface firing 57. 

Sweet potato 

black rot 291, blue mold 295, 
dry rot 294, lasiodiplodiose 294, 
leaf blight 295, leaf spot 295, 
nectriose 294, penicilliose 295, 
phyllostictose 295, scurf 295, 
soft rot 289, soil rot 293, stem 
rot 294, white rust 296, wilt 
294. 

Sycamore 

gnomoniose 448, powdery mil- 
dew 449. 

Symptons of disease 14. 

Synchytrium Vaccinii 149. 

Tall oat grass 397. 
Tank sprayers 42. 
Taphrina ccerulescens 444. 
Taphrinose 444. 
Tar spot 

maple 443, willow 450. 
Teosinte 365. 

rust 365, smut 365. 



Texas root rot 62. 

alfalfa 381, apple 97, cotton 401," 
fig 191, peach 133, pear 110. 

Thelephora 

galactina 427, pedicellata 109. 

Thelephorose 427. 
pear 109. 

Thielavia basicola 240, 296, 481. 

Thielaviose 481. 

Thoroughness in spraying 53. 

Tilletia 

fcetans 368, horrida 355, Tritici 
368. 

Timber and trees 409. 

Timber rot 233. 

Timothy 

anthracnose 397, rust 397, smut 
397. 

Tipburn 279. 

Tobacco 13, 296. 

rhizoctoniose 305, root rot 296, 
sclerotiniose 305, stem rot 305, 
white speck 304, wilt 13, 23, 
pole burn 305, pole rot 305, Oro- 
banche 307, mosaic 306, Gran- 
ville wilt 300, frenching 306, 
damping off 305, drop 305, 
calico 306, cercosporose 303, 
bacillose 300, bed rot 305, 
brown spot 304. 

Tomato 307. 

anthracnose 313, bacillose 307, 
black spot 312, blight 307, 311, 
blossom-end rot 312, cost of 
spraying 46, cylindrosporiose 
311, damping off 113, downy 
mildew 311, fumagose 313, 
fusariose 307, leaf mold 319, leaf 
spot 311, mosaic 314, (Edema 
313, point rot 312, rosette 314, 
rust 312, southern blight 313, 
wilt 307, 308. 
Trametes pini 414. 
Trees and timber 409. 

special hosts 431. 
Tropical fruits 184. 



512 



INDEX 



Tumor 464. 

Turnip 314. 

black rot 314, club root 315, 
downy mildew 315, macro- 
sporiose 315, powdery mildew 
315, scab 315, white rust 315. 

Twig blight 445. 

Uncinula 

necator 164, salicis 451. 

Uncinulose 

elm 439, grape 164, poplar 447, 
willow 451. 

Uredo Fici 191. 

Urocystis 

Agropyri 396, cepulse 247. 

Urocystose 396. 

Uromyces 

appendiculatus 201, Betse 209, 
caryophyllinus 455, striatus 383, 
Trifolii 387. 

Ustilaginoidea virens 354. 

Ustilago 

Avense 343, 349, Crameri 343, 
Hordei 329, lsevis 349, nuda 
327, perennans 397, striaeformis 
397, Tritici 370, Zese 331. 

Valsa leucostoma 129. 

Variegated plants 451. 

Vegetable and field crops 194. 

Venturia 

inaequalis 74, pyrina 107. 

Verbena 478. 

Vermicularia 

circinans 252, dematium 239, 
effigurata 457, telephii 477, 
trichella 468. 

Vermiculariose 

carnation 457, ivy 468, onion 
252, sedum 477. 

Vetch 397. 

Violet 

alternariose 479, anthracnose 
481, cercosporose 478, leaf spot 
14, 479, 481, downy mildew 



481, glceosporiose 481, marsoni- 
ose 481, phyllostictose 481, 
rhizoctoniose 481, spot disease 
479, thielaviose 481, zygodes- 
mose 481. 

Virginia creeper 

phyllostictose 481, powdery mil- 
dew 482. 

Volutella 61. 

Dianthi 459, fructi 95. 

Volutellose 

apple 95, carnation 459. 

Walnut 449. 

anthracnose 449, blight 449, 
gnomoniose 449, pseudomonose 
449. 

Water lily 

cercosporose 482. 

Watermelon 

alternariose 318, anthracnose 
318, bacillose 317, cercosporose 
318, downy mildew 318, fusa- 
riose 315, mycosphserellose 317, 
resistant 10, wilt 315, 317. 

Wheat 

anthracnose 375, black stem rust 
365, bunt 14, leptosphseriose 376, 
loose smut 14, 370, orange leaf 
rust 367, powdery mildew 375, 
rust 14, 22, scab 376, septoriose 
376, smut 19, stinking smut 368. 

White heart rot 414. 

White rot 418, 421. 

ash 21, 431, beet 210, cabbage 
216, cedar 435, grape 174. 

White rust 

horse-radish 241, radish 285, 
salsify 286, sweet potato 296, 
turnip 315. 

White smut 
spinach 287. 

White speck 304. 

Willow 

powdery mildew 451, rust 450, 
tar spot 450, uncinulose 451. 



INDEX 



513 



Wilt 15. 

alfalfa 379, 380, aster 452, cab- 
bage 216, cantaloupe 218, 223, 
carnation 458, clover 386, col- 
lard 229, corn 339, cotton 398, 
cowpea 390, cucumber 233, 
egg plant 236, flax 406, ginseng 
238, 239, lettuce 242, pepper 259, 
potato 275, 277, squash 289, 
sweet potato 294, tomato 307, 
308, watermelon 315, 317. 

Wither tip 189. 

Wood rot 

apple 98, cherry 120. 



Worms 1. 

Yellowing 16. 

Yellow leaf blight 405. 

Yellow leaf disease 330. 
corn 342, oat 352. 

Yellow rust 191. 

Yellows 

almond 115, apricot 116, cherry 
119, peach 135, plum 143, rasp- 
berry 180, violet 481. 

Zygodesmus albidus 481. 



2l 



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